java.lang.Object
- smile.sort.QuickSelect

```
public class QuickSelect
extends java.lang.Object
```
Selection is asking for the k th smallest element out of n elements. This class implements the fastest general method for selection based on partitioning, exactly as done in the Quicksort algorithm.
The most common use of selection is in the statistical characterization of a set of data. One often wants to know the median element (quantile p = 1/2) in an array or the top and bottom quartile elements (quantile p = 1/4, 3/4).

Author:

Haifeng Li

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method	Description
`static double`	`median(double[] a)`	Find the median of an array of type double.
`static float`	`median(float[] a)`	Find the median of an array of type float.
`static int`	`median(int[] a)`	Find the median of an array of type integer.
`static <T extends java.lang.Comparable<? super T>> T`	`median(T[] a)`	Find the median of an array of type double.
`static double`	`q1(double[] a)`	Find the first quantile (p = 1/4) of an array of type double.
`static float`	`q1(float[] a)`	Find the first quantile (p = 1/4) of an array of type float.
`static int`	`q1(int[] a)`	Find the first quantile (p = 1/4) of an array of type integer.
`static <T extends java.lang.Comparable<? super T>> T`	`q1(T[] a)`	Find the first quantile (p = 1/4) of an array of type double.
`static double`	`q3(double[] a)`	Find the third quantile (p = 3/4) of an array of type double.
`static float`	`q3(float[] a)`	Find the third quantile (p = 3/4) of an array of type float.
`static int`	`q3(int[] a)`	Find the third quantile (p = 3/4) of an array of type integer.
`static <T extends java.lang.Comparable<? super T>> T`	`q3(T[] a)`	Find the third quantile (p = 3/4) of an array of type double.
`static double`	`select(double[] arr, int k)`	Given k in [0, n-1], returns an array value from arr such that k array values are less than or equal to the one returned.
`static float`	`select(float[] arr, int k)`	Given k in [0, n-1], returns an array value from arr such that k array values are less than or equal to the one returned.
`static int`	`select(int[] arr, int k)`	Given k in [0, n-1], returns an array value from arr such that k array values are less than or equal to the one returned.
`static <T extends java.lang.Comparable<? super T>> T`	`select(T[] arr, int k)`	Given k in [0, n-1], returns an array value from arr such that k array values are less than or equal to the one returned.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - select
```
public static int select(int[] arr,
                         int k)
```
    Given k in [0, n-1], returns an array value from arr such that k array values are less than or equal to the one returned. The input array will be rearranged to have this value in location arr[k], with all smaller elements moved to arr[0, k-1] (in arbitrary order) and all larger elements in arr[k+1, n-1] (also in arbitrary order).
  - select
```
public static float select(float[] arr,
                           int k)
```
    Given k in [0, n-1], returns an array value from arr such that k array values are less than or equal to the one returned. The input array will be rearranged to have this value in location arr[k], with all smaller elements moved to arr[0, k-1] (in arbitrary order) and all larger elements in arr[k+1, n-1] (also in arbitrary order).
  - select
```
public static double select(double[] arr,
                            int k)
```
    Given k in [0, n-1], returns an array value from arr such that k array values are less than or equal to the one returned. The input array will be rearranged to have this value in location arr[k], with all smaller elements moved to arr[0, k-1] (in arbitrary order) and all larger elements in arr[k+1, n-1] (also in arbitrary order).
  - select
```
public static <T extends java.lang.Comparable<? super T>> T select(T[] arr,
                                                                   int k)
```
    Given k in [0, n-1], returns an array value from arr such that k array values are less than or equal to the one returned. The input array will be rearranged to have this value in location arr[k], with all smaller elements moved to arr[0, k-1] (in arbitrary order) and all larger elements in arr[k+1, n-1] (also in arbitrary order).
  - median
```
public static int median(int[] a)
```
    Find the median of an array of type integer.
  - median
```
public static float median(float[] a)
```
    Find the median of an array of type float.
  - median
```
public static double median(double[] a)
```
    Find the median of an array of type double.
  - median
```
public static <T extends java.lang.Comparable<? super T>> T median(T[] a)
```
    Find the median of an array of type double.
  - q1
```
public static int q1(int[] a)
```
    Find the first quantile (p = 1/4) of an array of type integer.
  - q1
```
public static float q1(float[] a)
```
    Find the first quantile (p = 1/4) of an array of type float.
  - q1
```
public static double q1(double[] a)
```
    Find the first quantile (p = 1/4) of an array of type double.
  - q1
```
public static <T extends java.lang.Comparable<? super T>> T q1(T[] a)
```
    Find the first quantile (p = 1/4) of an array of type double.
  - q3
```
public static int q3(int[] a)
```
    Find the third quantile (p = 3/4) of an array of type integer.
  - q3
```
public static float q3(float[] a)
```
    Find the third quantile (p = 3/4) of an array of type float.
  - q3
```
public static double q3(double[] a)
```
    Find the third quantile (p = 3/4) of an array of type double.
  - q3
```
public static <T extends java.lang.Comparable<? super T>> T q3(T[] a)
```
    Find the third quantile (p = 3/4) of an array of type double.

Class QuickSelect

Method Summary

Methods inherited from class java.lang.Object

Method Detail

select

select

select

select

median

median

median

median

q1

q1

q1

q1

q3

q3

q3

q3