edu.princeton.cs.algs4

## Class StdStats

• Object
• edu.princeton.cs.algs4.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

Methods
Modifier and Type Method and 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 Object

`clone, equals, finalize, 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, an–1) to standard draw.
Parameters:
`a` - the array of values
• #### plotLines

`public static void plotLines(double[] a)`
Plots the line segments connecting (i, ai) to (i+1, ai+1) for each i to standard draw.
Parameters:
`a` - the array of values
• #### plotBars

`public static void plotBars(double[] a)`
Plots bars from (0, ai) to (ai) 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