Class SequenceSampler


  • public final class SequenceSampler
    extends Object
    ArraySampler is a class of utility methods related to efficiently generating random samples of array elements, without replacement.
    • Method Summary

      All Methods Static Methods Concrete Methods 
      Modifier and Type Method Description
      static byte[] sample​(byte[] source, double p)
      Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.
      static byte[] sample​(byte[] source, int k, byte[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static char[] sample​(char[] source, double p)
      Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.
      static char[] sample​(char[] source, int k, char[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static double[] sample​(double[] source, double p)
      Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.
      static double[] sample​(double[] source, int k, double[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static float[] sample​(float[] source, double p)
      Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.
      static float[] sample​(float[] source, int k, float[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static int[] sample​(int[] source, double p)
      Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.
      static int[] sample​(int[] source, int k, int[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static long[] sample​(long[] source, double p)
      Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.
      static long[] sample​(long[] source, int k, long[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static short[] sample​(short[] source, double p)
      Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.
      static short[] sample​(short[] source, int k, short[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static char[] sample​(String source, double p)
      Generates a random sample, without replacement, from a given String with a specified probability of a character's inclusion in the sample.
      static char[] sample​(String source, int k, char[] target)
      Generates a random sample of k chars, without replacement, from a given source String.
      static <T> T[] sample​(T[] source, double p)
      Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.
      static <T> T[] sample​(T[] source, int k, T[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static byte[] sampleInsertion​(byte[] source, int k, byte[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static char[] sampleInsertion​(char[] source, int k, char[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static double[] sampleInsertion​(double[] source, int k, double[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static float[] sampleInsertion​(float[] source, int k, float[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static int[] sampleInsertion​(int[] source, int k, int[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static long[] sampleInsertion​(long[] source, int k, long[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static short[] sampleInsertion​(short[] source, int k, short[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static char[] sampleInsertion​(String source, int k, char[] target)
      Generates a random sample of k chars, without replacement, from a given source String.
      static <T> T[] sampleInsertion​(T[] source, int k, T[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static byte[] samplePool​(byte[] source, int k, byte[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static char[] samplePool​(char[] source, int k, char[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static double[] samplePool​(double[] source, int k, double[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static float[] samplePool​(float[] source, int k, float[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static int[] samplePool​(int[] source, int k, int[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static long[] samplePool​(long[] source, int k, long[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static short[] samplePool​(short[] source, int k, short[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static char[] samplePool​(String source, int k, char[] target)
      Generates a random sample of k chars, without replacement, from a given source String.
      static <T> T[] samplePool​(T[] source, int k, T[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static byte[] sampleReservoir​(byte[] source, int k, byte[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static char[] sampleReservoir​(char[] source, int k, char[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static double[] sampleReservoir​(double[] source, int k, double[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static float[] sampleReservoir​(float[] source, int k, float[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static int[] sampleReservoir​(int[] source, int k, int[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static long[] sampleReservoir​(long[] source, int k, long[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static short[] sampleReservoir​(short[] source, int k, short[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
      static char[] sampleReservoir​(String source, int k, char[] target)
      Generates a random sample of k chars, without replacement, from a given source String.
      static <T> T[] sampleReservoir​(T[] source, int k, T[] target)
      Generates a random sample of k elements, without replacement, from a given source array.
    • Method Detail

      • sample

        public static byte[] sample​(byte[] source,
                                    double p)

        Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.

        Parameters:
        source - The array from which to sample.
        p - The probability that element is included in the sample. The expected sample size is source.length * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static char[] sample​(char[] source,
                                    double p)

        Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.

        Parameters:
        source - The array from which to sample.
        p - The probability that element is included in the sample. The expected sample size is source.length * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static double[] sample​(double[] source,
                                      double p)

        Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.

        Parameters:
        source - The array from which to sample.
        p - The probability that element is included in the sample. The expected sample size is source.length * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static float[] sample​(float[] source,
                                     double p)

        Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.

        Parameters:
        source - The array from which to sample.
        p - The probability that element is included in the sample. The expected sample size is source.length * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static int[] sample​(int[] source,
                                   double p)

        Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.

        Parameters:
        source - The array from which to sample.
        p - The probability that element is included in the sample. The expected sample size is source.length * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static long[] sample​(long[] source,
                                    double p)

        Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.

        Parameters:
        source - The array from which to sample.
        p - The probability that element is included in the sample. The expected sample size is source.length * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static short[] sample​(short[] source,
                                     double p)

        Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.

        Parameters:
        source - The array from which to sample.
        p - The probability that element is included in the sample. The expected sample size is source.length * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static char[] sample​(String source,
                                    double p)

        Generates a random sample, without replacement, from a given String with a specified probability of a character's inclusion in the sample.

        Parameters:
        source - The String from which to sample.
        p - The probability that a character is included in the sample. The expected sample size is source.length() * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static <T> T[] sample​(T[] source,
                                     double p)

        Generates a random sample, without replacement, from a given source array with a specified probability of an element's inclusion in the sample.

        Type Parameters:
        T - The type of array elements.
        Parameters:
        source - The array from which to sample.
        p - The probability that element is included in the sample. The expected sample size is source.length * p.
        Returns:
        An array containing the sample, whose sample size is simply the length of the array.
      • sample

        public static int[] sample​(int[] source,
                                   int k,
                                   int[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sample

        public static long[] sample​(long[] source,
                                    int k,
                                    long[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sample

        public static short[] sample​(short[] source,
                                     int k,
                                     short[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sample

        public static byte[] sample​(byte[] source,
                                    int k,
                                    byte[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sample

        public static char[] sample​(char[] source,
                                    int k,
                                    char[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sample

        public static char[] sample​(String source,
                                    int k,
                                    char[] target)

        Generates a random sample of k chars, without replacement, from a given source String. All n choose k combinations are equally likely, where n is the length of the source String.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length()).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length()
        NegativeArraySizeException - if k < 0
      • sample

        public static double[] sample​(double[] source,
                                      int k,
                                      double[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sample

        public static float[] sample​(float[] source,
                                     int k,
                                     float[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sample

        public static <T> T[] sample​(T[] source,
                                     int k,
                                     T[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This method chooses among the ArraySampler.samplePool, ArraySampler.sampleReservoir, and ArraySampler.sampleInsertion methods based on the values of source.length and k.

        The runtime is O(min(n, k2)) and it generates O(min(k, n-k)) random numbers.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Type Parameters:
        T - The type of array elements.
        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static int[] sampleReservoir​(int[] source,
                                            int k,
                                            int[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static long[] sampleReservoir​(long[] source,
                                             int k,
                                             long[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static short[] sampleReservoir​(short[] source,
                                              int k,
                                              short[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static byte[] sampleReservoir​(byte[] source,
                                             int k,
                                             byte[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static char[] sampleReservoir​(char[] source,
                                             int k,
                                             char[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static char[] sampleReservoir​(String source,
                                             int k,
                                             char[] target)

        Generates a random sample of k chars, without replacement, from a given source String. All n choose k combinations are equally likely, where n is the length of the source String.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length()).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length()
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static double[] sampleReservoir​(double[] source,
                                               int k,
                                               double[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static float[] sampleReservoir​(float[] source,
                                              int k,
                                              float[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleReservoir

        public static <T> T[] sampleReservoir​(T[] source,
                                              int k,
                                              T[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        Uses the reservoir sampling algorithm (Algorithm R) from J. Vitter's 1985 article "Random Sampling with a Reservoir" from ACM Transactions on Mathematical Software. The runtime is O(n) and it generates O(n-k) random numbers. Thus, it is an especially good choice as k approaches n. Only constant extra space required.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Type Parameters:
        T - The type of array elements.
        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • samplePool

        public static int[] samplePool​(int[] source,
                                       int k,
                                       int[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • samplePool

        public static long[] samplePool​(long[] source,
                                        int k,
                                        long[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • samplePool

        public static short[] samplePool​(short[] source,
                                         int k,
                                         short[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • samplePool

        public static byte[] samplePool​(byte[] source,
                                        int k,
                                        byte[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • samplePool

        public static char[] samplePool​(char[] source,
                                        int k,
                                        char[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • samplePool

        public static char[] samplePool​(String source,
                                        int k,
                                        char[] target)

        Generates a random sample of k chars, without replacement, from a given source String. All n choose k combinations are equally likely, where n is the length of the source String.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source to sample.
        k - The number of random samples (must be no greater than source.length()).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length()
        NegativeArraySizeException - if k < 0
      • samplePool

        public static double[] samplePool​(double[] source,
                                          int k,
                                          double[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • samplePool

        public static float[] samplePool​(float[] source,
                                         int k,
                                         float[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • samplePool

        public static <T> T[] samplePool​(T[] source,
                                         int k,
                                         T[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        This implements the algorithm SELECT of S. Goodman and S. Hedetniemi, as described in: J Ernvall, O Nevalainen, "An Algorithm for Unbiased Random Sampling," The Computer Journal, 25(1):45-47, 1982.

        The runtime is O(n) and it generates O(k) random numbers. Thus, it is a better choice than sampleReservoir when k < n-k. However, this uses O(n) extra space, whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Type Parameters:
        T - The type of array elements.
        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static int[] sampleInsertion​(int[] source,
                                            int k,
                                            int[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. Just like sampleReservoir, the sampleInsertion method only requires O(1) extra space, while samplePool requires O(n) extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static long[] sampleInsertion​(long[] source,
                                             int k,
                                             long[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. However, this uses O(k) extra space (better than samplePool), whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static short[] sampleInsertion​(short[] source,
                                              int k,
                                              short[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. However, this uses O(k) extra space (better than samplePool), whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static byte[] sampleInsertion​(byte[] source,
                                             int k,
                                             byte[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. However, this uses O(k) extra space (better than samplePool), whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static char[] sampleInsertion​(char[] source,
                                             int k,
                                             char[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. However, this uses O(k) extra space (better than samplePool), whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static char[] sampleInsertion​(String source,
                                             int k,
                                             char[] target)

        Generates a random sample of k chars, without replacement, from a given source String. All n choose k combinations are equally likely, where n is the length of the source String.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. However, this uses O(k) extra space (better than samplePool), whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source to sample.
        k - The number of random samples (must be no greater than source.length()).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length()
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static double[] sampleInsertion​(double[] source,
                                               int k,
                                               double[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. However, this uses O(k) extra space (better than samplePool), whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static float[] sampleInsertion​(float[] source,
                                              int k,
                                              float[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. However, this uses O(k) extra space (better than samplePool), whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0
      • sampleInsertion

        public static <T> T[] sampleInsertion​(T[] source,
                                              int k,
                                              T[] target)

        Generates a random sample of k elements, without replacement, from a given source array. All n choose k combinations are equally likely, where n is the length of the source array.

        The runtime is O(k2) and it generates O(k) random numbers. Thus, it is a better choice than both sampleReservoir and samplePool when k2 < n. However, this uses O(k) extra space (better than samplePool), whereas the reservoir algorithm uses no extra space.

        This method is safe to use with threads, as it uses ThreadLocalRandom as the underlying source of randomness.

        Type Parameters:
        T - The type of array elements.
        Parameters:
        source - The source array to sample.
        k - The number of random samples (must be no greater than source.length).
        target - An array to hold the result. If target is null or target.length is less than k, then this method will construct a new array for the result.
        Returns:
        An array containing the random sample.
        Throws:
        IllegalArgumentException - if k > source.length
        NegativeArraySizeException - if k < 0