This module provides basic functions used in descriptive statistics. It 
borrows very heavily from Statistics::Descriptive::Full (which is included 
with Statistics::Descriptive) with one major difference. This module is 
optimized for discretized data e.g. data from an A/D conversion that has a 
discrete set of possible values. E.g. if your data is produced by an 8 bit 
A/D then you'd have only 256 possible values in your data set. Even though 
you might have a million data points, you'd only have 256 different values 
in those million points. Instead of storing the entire data set as 
Statistics::Descriptive does, this module only stores the values it's seen 
and the number of times it's seen each value.

For very large data sets, this storage method results in significant speed 
and memory improvements. In a test case with 2.6 million data points from 
a real world application, Statistics::Descriptive::Discrete took 40 
seconds to calculate a set of statistics instead of the 561 seconds 
required by Statistics::Descriptive::Full. It also required only 4MB of 
RAM instead of the 400MB used by Statistics::Descriptive::Full for the 
same data set.

WWW: http://search.cpan.org/dist/Statistics-Descriptive-Discrete/