Class StdStats

Object

StdStats

public final class StdStats
extends Object

The StdStats class provides static methods for computing statistics such as min, max, mean, sample standard deviation, and sample variance.

For additional documentation, see Section 2.2 of Computer Science: An Interdisciplinary Approach by Robert Sedgewick and Kevin Wayne.

Author:

Robert Sedgewick, Kevin Wayne

Method Summary

Modifier and Type	Method	Description
static void	main(String[] args)	Unit tests StdStats.
static double	max(double[] a)	Returns the maximum value in the specified array.
static double	max(double[] a, int lo, int hi)	Returns the maximum value in the specified subarray.
static int	max(int[] a)	Returns the maximum value in the specified array.
static double	mean(double[] a)	Returns the average value in the specified array.
static double	mean(double[] a, int lo, int hi)	Returns the average value in the specified subarray.
static double	mean(int[] a)	Returns the average value in the specified array.
static double	min(double[] a)	Returns the minimum value in the specified array.
static double	min(double[] a, int lo, int hi)	Returns the minimum value in the specified subarray.
static int	min(int[] a)	Returns the minimum value in the specified array.
static void	plotBars(double[] a)	Plots bars from (0, ai) to (ai) for each i to standard draw.
static void	plotLines(double[] a)	Plots the line segments connecting (i, ai) to (i+1, ai+1) for each i to standard draw.
static void	plotPoints(double[] a)	Plots the points (0, a0), (1, a1), ..., (n-1, an-1) to standard draw.
static double	stddev(double[] a)	Returns the sample standard deviation in the specified array.
static double	stddev(double[] a, int lo, int hi)	Returns the sample standard deviation in the specified subarray.
static double	stddev(int[] a)	Returns the sample standard deviation in the specified array.
static double	stddevp(double[] a)	Returns the population standard deviation in the specified array.
static double	stddevp(double[] a, int lo, int hi)	Returns the population standard deviation in the specified subarray.
static double	var(double[] a)	Returns the sample variance in the specified array.
static double	var(double[] a, int lo, int hi)	Returns the sample variance in the specified subarray.
static double	var(int[] a)	Returns the sample variance in the specified array.
static double	varp(double[] a)	Returns the population variance in the specified array.
static double	varp(double[] a, int lo, int hi)	Returns the population variance in the specified subarray.

Methods inherited from class java.lang.Object

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

Method Detail

max

public static double max(double[] a)

Returns the maximum value in the specified array.

Parameters:

a - the array

Returns:

the maximum value in the array a[]; Double.NEGATIVE_INFINITY if no such value

max

public static double max(double[] a,
                         int lo,
                         int hi)

Returns the maximum value in the specified subarray.

Parameters:

a - the array

lo - the left endpoint of the subarray (inclusive)

hi - the right endpoint of the subarray (exclusive)

Returns:

the maximum value in the subarray a[lo..hi); Double.NEGATIVE_INFINITY if no such value

Throws:

IllegalArgumentException - if a is null

IllegalArgumentException - unless (0 <= lo) && (lo < hi) && (hi <= a.length)

max

public static int max(int[] a)

Returns the maximum value in the specified array.

Parameters:

a - the array

Returns:

the maximum value in the array a[]; Integer.MIN_VALUE if no such value

min

public static double min(double[] a)

Returns the minimum value in the specified array.

Parameters:

a - the array

Returns:

the minimum value in the array a[]; Double.POSITIVE_INFINITY if no such value

min

public static double min(double[] a,
                         int lo,
                         int hi)

Returns the minimum value in the specified subarray.

Parameters:

a - the array

lo - the left endpoint of the subarray (inclusive)

hi - the right endpoint of the subarray (exclusive)

Returns:

the maximum value in the subarray a[lo..hi); Double.POSITIVE_INFINITY if no such value

Throws:

IllegalArgumentException - if a is null

IllegalArgumentException - unless (0 <= lo) && (lo < hi) && (hi <= a.length)

min

public static int min(int[] a)

Returns the minimum value in the specified array.

Parameters:

a - the array

Returns:

the minimum value in the array a[]; Integer.MAX_VALUE if no such value

mean

public static double mean(double[] a)

Returns the average value in the specified array.

Parameters:

a - the array

Returns:

the average value in the array a[]; Double.NaN if no such value

mean

public static double mean(double[] a,
                          int lo,
                          int hi)

Returns the average value in the specified subarray.

Parameters:

a - the array

lo - the left endpoint of the subarray (inclusive)

hi - the right endpoint of the subarray (exclusive)

Returns:

the average value in the subarray a[lo..hi); Double.NaN if no such value

Throws:

IllegalArgumentException - if a is null

IllegalArgumentException - unless (0 <= lo) && (lo < hi) && (hi <= a.length)

mean

public static double mean(int[] a)

Returns the average value in the specified array.

Parameters:

a - the array

Returns:

the average value in the array a[]; Double.NaN if no such value

var

public static double var(double[] a)

Returns the sample variance in the specified array.

Parameters:

a - the array

Returns:

the sample variance in the array a[]; Double.NaN if no such value

var

public static double var(double[] a,
                         int lo,
                         int hi)

Returns the sample variance in the specified subarray.

Parameters:

a - the array

lo - the left endpoint of the subarray (inclusive)

hi - the right endpoint of the subarray (exclusive)

Returns:

the sample variance in the subarray a[lo..hi); Double.NaN if no such value

Throws:

IllegalArgumentException - if a is null

IllegalArgumentException - unless (0 <= lo) && (lo < hi) && (hi <= a.length)

var

public static double var(int[] a)

Returns the sample variance in the specified array.

Parameters:

a - the array

Returns:

the sample variance in the array a[]; Double.NaN if no such value

varp

public static double varp(double[] a)

Returns the population variance in the specified array.

Parameters:

a - the array

Returns:

the population variance in the array a[]; Double.NaN if no such value

varp

public static double varp(double[] a,
                          int lo,
                          int hi)

Returns the population variance in the specified subarray.

Parameters:

a - the array

lo - the left endpoint of the subarray (inclusive)

hi - the right endpoint of the subarray (exclusive)

Returns:

the population variance in the subarray a[lo..hi); Double.NaN if no such value

Throws:

IllegalArgumentException - if a is null

IllegalArgumentException - unless (0 <= lo) && (lo < hi) && (hi <= a.length)

stddev

public static double stddev(double[] a)

Returns the sample standard deviation in the specified array.

Parameters:

a - the array

Returns:

the sample standard deviation in the array a[]; Double.NaN if no such value

stddev

public static double stddev(int[] a)

Returns the sample standard deviation in the specified array.

Parameters:

a - the array

Returns:

the sample standard deviation in the array a[]; Double.NaN if no such value

stddev

public static double stddev(double[] a,
                            int lo,
                            int hi)

Returns the sample standard deviation in the specified subarray.

Parameters:

a - the array

lo - the left endpoint of the subarray (inclusive)

hi - the right endpoint of the subarray (exclusive)

Returns:

the sample standard deviation in the subarray a[lo..hi); Double.NaN if no such value

Throws:

IllegalArgumentException - if a is null

IllegalArgumentException - unless (0 <= lo) && (lo < hi) && (hi <= a.length)

stddevp

public static double stddevp(double[] a)

Returns the population standard deviation in the specified array.

Parameters:

a - the array

Returns:

the population standard deviation in the array; Double.NaN if no such value

stddevp

public static double stddevp(double[] a,
                             int lo,
                             int hi)

Returns the population standard deviation in the specified subarray.

Parameters:

a - the array

lo - the left endpoint of the subarray (inclusive)

hi - the right endpoint of the subarray (exclusive)

Returns:

the population standard deviation in the subarray a[lo..hi); Double.NaN if no such value

Throws:

IllegalArgumentException - if a is null

IllegalArgumentException - unless (0 <= lo) && (lo < hi) && (hi <= a.length)

plotPoints

public static void plotPoints(double[] a)

Plots the points (0, a₀), (1, a₁), ..., (n-1, a_n-1) to standard draw.

Parameters:

a - the array of values

plotLines

public static void plotLines(double[] a)

Plots the line segments connecting (i, a_i) to (i+1, a_i+1) for each i to standard draw.

Parameters:

a - the array of values

plotBars

public static void plotBars(double[] a)

Plots bars from (0, a_i) to (a_i) for each i to standard draw.

Parameters:

a - the array of values

main

public static void main(String[] args)

Unit tests StdStats. Convert command-line arguments to array of doubles and call various methods.

Parameters:

args - the command-line arguments