NAME

Statistics::TopK - Implementation of the top-k streaming algorithm

SYNOPSIS

    use Statistics::TopK;

    my $counter = Statistics::TopK->new(10);
    while (my $val = <STDIN>) {
        chomp $val;
        $counter->add($val);
    }
    my @top = $counter->top;
    my %counts = $counter->counts;

DESCRIPTION

The Statistics::TopK module implements the top-k streaming algorithm, also know as the "heavy hitters" algorithm. It is designed to process data streams and probabilistally calculate the k most frequent items while using limited memory.

A typical example would be to determine the top 10 IP addresses listed in an access log. A simple solution would be to hash each IP address to a counter and then sort the resulting hash by the counter size. But the hash could theoretically require over 4 billion keys.

The top-k algorithm only requires storage space proportional to the number of items of interest. It accomplishes this by sacrificing precision, as it is only a probabilistic counter.

METHODS

new

    $counter = Statistics::TopK->new($k)

Creates a new Statistics::TopK object which is prepared to count the top $k elements.

add

    $count = $counter->add($element)

Count the given $element and return its approximate count (if any) in the Statistics::TopK object.

Note that adding an element does not guarantee it will be counted yet, as the algorithm is probabilistic, and the occurrence of the current element might only be used decrease the count of one of the current top elements.

top

    @top = $counter->top()

Returns a list of the top-k counted elements.

counts

    %counts = $counter->counts()

Returns a hash of the top-k counted elements and their counts.

SEE ALSO

http://en.wikipedia.org/wiki/Streaming_algorithm#Heavy_hitters

REQUESTS AND BUGS

Please report any bugs or feature requests to http://rt.cpan.org/Public/Bug/Report.html?Queue=Statistics-TopK. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

    perldoc Statistics::TopK

You can also look for information at:

COPYRIGHT AND LICENSE

Copyright (C) 2009-2015 gray <gray at cpan.org>, all rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

AUTHOR

gray, <gray at cpan.org>