Package org.apache.datasketches

Class QuickSelect

java.lang.Object
org.apache.datasketches.QuickSelect
public final class QuickSelect
extends Object
QuickSelect algorithm improved from Sedgewick. Gets the kth order value (1-based or 0-based) from the array. Warning! This changes the ordering of elements in the given array!
Also see:
blog.teamleadnet.com/2012/07/quick-select-algorithm-find-kth-element.html
See QuickSelectTest for examples and testNG tests.
Author:
Lee Rhodes

  • Method Summary

    Modifier and Type Method Description
    static double select​(double[] arr, int lo, int hi, int pivot)
    Gets the 0-based kth order statistic from the array.
    static long select​(long[] arr, int lo, int hi, int pivot)
    Gets the 0-based kth order statistic from the array.
    static double selectExcludingZeros​(double[] arr, int nonZeros, int pivot)
    Gets the 1-based kth order statistic from the array excluding any zero values in the array.
    static long selectExcludingZeros​(long[] arr, int nonZeros, int pivot)
    Gets the 1-based kth order statistic from the array excluding any zero values in the array.
    static double selectIncludingZeros​(double[] arr, int pivot)
    Gets the 1-based kth order statistic from the array including any zero values in the array.
    static long selectIncludingZeros​(long[] arr, int pivot)
    Gets the 1-based kth order statistic from the array including any zero values in the array.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Method Details

    • select

      public static long select​(long[] arr, int lo, int hi, int pivot)
      Gets the 0-based kth order statistic from the array. Warning! This changes the ordering of elements in the given array!
      Parameters:
      arr - The array to be re-arranged.
      lo - The lowest 0-based index to be considered.
      hi - The highest 0-based index to be considered.
      pivot - The 0-based index of the value to pivot on.
      Returns:
      The value of the smallest (n)th element where n is 0-based.

    • selectIncludingZeros

      public static long selectIncludingZeros​(long[] arr, int pivot)
      Gets the 1-based kth order statistic from the array including any zero values in the array. Warning! This changes the ordering of elements in the given array!
      Parameters:
      arr - The hash array.
      pivot - The 1-based index of the value that is chosen as the pivot for the array. After the operation all values below this 1-based index will be less than this value and all values above this index will be greater. The 0-based index of the pivot will be pivot-1.
      Returns:
      The value of the smallest (N)th element including zeros, where N is 1-based.

    • selectExcludingZeros

      public static long selectExcludingZeros​(long[] arr, int nonZeros, int pivot)
      Gets the 1-based kth order statistic from the array excluding any zero values in the array. Warning! This changes the ordering of elements in the given array!
      Parameters:
      arr - The hash array.
      nonZeros - The number of non-zero values in the array.
      pivot - The 1-based index of the value that is chosen as the pivot for the array. After the operation all values below this 1-based index will be less than this value and all values above this index will be greater. The 0-based index of the pivot will be pivot+arr.length-nonZeros-1.
      Returns:
      The value of the smallest (N)th element excluding zeros, where N is 1-based.

    • select

      public static double select​(double[] arr, int lo, int hi, int pivot)
      Gets the 0-based kth order statistic from the array. Warning! This changes the ordering of elements in the given array!
      Parameters:
      arr - The array to be re-arranged.
      lo - The lowest 0-based index to be considered.
      hi - The highest 0-based index to be considered.
      pivot - The 0-based smallest value to pivot on.
      Returns:
      The value of the smallest (n)th element where n is 0-based.

    • selectIncludingZeros

      public static double selectIncludingZeros​(double[] arr, int pivot)
      Gets the 1-based kth order statistic from the array including any zero values in the array. Warning! This changes the ordering of elements in the given array!
      Parameters:
      arr - The hash array.
      pivot - The 1-based index of the value that is chosen as the pivot for the array. After the operation all values below this 1-based index will be less than this value and all values above this index will be greater. The 0-based index of the pivot will be pivot-1.
      Returns:
      The value of the smallest (N)th element including zeros, where N is 1-based.

    • selectExcludingZeros

      public static double selectExcludingZeros​(double[] arr, int nonZeros, int pivot)
      Gets the 1-based kth order statistic from the array excluding any zero values in the array. Warning! This changes the ordering of elements in the given array!
      Parameters:
      arr - The hash array.
      nonZeros - The number of non-zero values in the array.
      pivot - The 1-based index of the value that is chosen as the pivot for the array. After the operation all values below this 1-based index will be less than this value and all values above this index will be greater. The 0-based index of the pivot will be pivot+arr.length-nonZeros-1.
      Returns:
      The value of the smallest (N)th element excluding zeros, where N is 1-based.