Jakarta Commons Cookbook

8.6. Calculating Simple Univariate Statistics

Problem

You need to calculate univariate statistics such as mean, median, variance, minimum and maximum.

Solution

Use Commons Math’s StatUtils to calculate simple univariate statistics. The following example uses StatUtils to calculate simple statistics for a double[]:

import org.apache.commons.math.stat.StatUtils;

double[] values = new double[] { 2.3, 5.4, 6.2, 7.3, 23.3 };

System.out.println( "min: " + StatUtils.min( values ) );
System.out.println( "max: " + StatUtils.max( values ) );
System.out.println( "mean: " + StatUtils.mean( values ) );
System.out.println( "product: " + StatUtils.product( values ) );
System.out.println( "sum: " + StatUtils.sum( values ) );
System.out.println( "variance: " + StatUtils.variance( values ) );

This code executes and prints a few simple statistics to the console, as follows:

min: 2.3
max: 23.3
mean: 8.9
product: 13097.61036
sum: 44.5
variance: 68.25500000000001

Discussion

StatUtils delegates these calculations to functors in the org.apache.commons.math.stat.univariate.moment, org.apache.commons.math.stat.univariate.rank, and org.apache.commons.math.stat.univariate.summary packages. The following example uses the individual classes from these packages to recreate the previous example, and it adds some measures not available in StatUtil:

import org.apache.commons.math.stat.univariate.moment.*; import org.apache.commons.math.stat.univariate.rank.*; import org.apache.commons.math.stat.univariate.summary.*; ...