Array::Windowed - return a windowed slice of the array


   use Array::Windowed qw(windowed_array);

   # from an array
   my $new_array = array_window @old_array, $start_index, $count);

   # from an arrayref
   my $new_array2 = &array_window($array_ref, $start_index, $count);


Simple module to return a slice of the passed array as specified by a start position and a number of elements. Unlike the built in slicing functions this does not populate the returned array with undefs for out of bounds operations, but simply returns a smaller array.


Exported on demand (or you can call it fully qualified)

array_windowed @old_array, $start_index, $count

Returns an array reference containing up to $count elements from the @old_array starting at $start_index.

Unlike a traditional array slice elements outside the bounds of the array are simply dropped. Negative indexes are treated as normal indexes that occur before the 0th index (rather than indexes counting backwards from the start of the array.)

This is probably best shown with a series of examples:

        my @array = ['a'..'z'];

        # ["a".."z"]
        array_windowed(@array, 0, 26);

        # ["a","b","c","d","e"]
        array_windowed(@array, 0, 5);

        # ["b","c","d","e","f"]
        array_windowed(@array, 1, 5);

        # []
        array_windowed(@array, 26, 5);

        # []
        array_windowed(@array, -50, 5);

        # ["x","y","z"]
        array_windowed(@array, 23, 5);

        # ["a","b","c"]
        array_windowed(@array, -2, 5); 

        # ["a".."z"]
        &array_windowed(\@array, 0, 26);


Why this module?

Why not simple array slices with @foo[ ... ]

Because the edge cases of indexes outside the bounds of the array don't do the same thing (they return lots of undefs mainly)

Why not splice?

It's destructive on the original array.

Why not Array::Window

Because it tries too hard to DTRT, which isn't the RT for us. For example, if you have a count bigger than the entire array then it always returns the entire array irregardless of the start position.

This doesn't mean it's not the module for you, however.

Why not Data::Page

This concept of windowing we're using doesn't use pages, but rather a start position and a count.

This doesn't mean it's not the module for you, however.


Written by Mark Fowler <>


Copyright Mark Fowler 2012. All Rights Reserved.

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


This module does no sanity checking on the values that are passed into it (i.e. it does not check that $start or $count are integer numbers, nor does it check that the first argument is an array reference if you disable prototyping.)

Bugs should be reported via this distribution's CPAN RT queue. This can be found at

You can also address issues by forking this distribution on github and sending pull requests. It can be found at


Array::Window, Data::Page