## 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

All Methods
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, 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