Author image Luc St-Louis


Data::RandomKeep - Randomly keep a given number of offered items.


    use Data::RandomKeep;

        # Keep 10 random lines from a file.
    my $lines_keeper = Data::RandomKeep->new(10)
    $lines_keeper->offer($_) while <$file_hdl>;
    my $kept_lines_array_ref = $lines_keeper->kept();

        # Select 6 numbers out of 49 as a pick for a lottery ticket.
    my $numbers_keeper = Data::RandomKeep->new(6);
    $numbers_keeper->offer(1 .. 49);
    print "This might win: @{$numbers_keeper->kept()}\n";


Suppose you want to keep ten random lines from a file. You might read all the lines in an array, shuffle it, and keep the first ten lines, but that can be quite wasteful, especially if the file is big. This module implements the task in a more efficient manner.

To use the module, you first instantiate a Data::RandomKeep object, telling the constructor how many items you will want to keep. Then you offer() it items, which the object will keep or discard, with correct randomness. At any moment, you can look at the items that have been kept up to that point, using the kept() method.


$pkg->new ($nb_to_keep)

Returns a ref to a newly created Data::RandomKeep object, designed to keep a maximum of $nb_to_keep items. If $nb_to_keep is not defined, a single item will eventually be kept.

$self->offer (@items)

Offers @items for inclusion into the set of kept items. The decision to keep it will be statistically correct, given the total number of items the instance is supposed to keep and the number of items offered so far.

$self->kept ()

Returns a ref to an array of the items kept so far. The items will be in the same order in which they were originally offered.


Luc St-Louis, <>


Copyright (C) 2008 by Luc St-Louis

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.3 or, at your option, any later version of Perl 5 you may have available.