Edmund von der Burg

NAME

List::Search - fast searching of sorted lists

SYNOPSIS

    use List::Search qw( list_search nlist_search custom_list_search );

    # Create a list to search
    my @list = sort qw( bravo charlie delta );

    # Search for a value, returns the index of first match
    print list_search( 'alpha',   \@list );    #  0
    print list_search( 'charlie', \@list );    #  1
    print list_search( 'zebra',   \@list );    #  -1

    # Search numerically
    my @numbers = sort { $a <=> $b } ( 10, 20, 100, 200, );
    print nlist_search( 20, \@numbers );       #  2

    # Search using some other comparison
    my $cmp_code = sub { lc( $_[0] ) cmp lc( $_[1] ) };
    my @custom_list = sort { $cmp_code->( $a, $b ) } qw( FOO bar BAZ bundy );
    print list_search_generic( $cmp_code, 'foo', \@custom_list );

DESCRIPTION

This module lets you quickly search a sorted list. It will return the index of the first entry that matches, or if there is no exact matches then the first entry that is greater than the search key.

For example in the list my @list = qw( bob dave fred ); searching for dave will return 1 as $list[1] eq 'dave'. Searching for charles will also return 1 as dave is the first entry that is greater than charles.

If there are none of the entries match then -1 is returned. You can either check for this or use it as an index to get the last values in the list. Whichever approach you choose will depend on what you are trying to do.

The actual searching is done using a binary search which is very fast.

METHODS

  my $idx = list_search( $key, \@sorted_list );

Searches the list using cmp as the comparison operator. Returns the index of the first entry that is equal to or greater than $key. If there is no match then returns -1.

  my $idx = nlist_search( $key, \@sorted_list );

Searches the list using <=> as the comparison operator. Returns the index of the first entry that is equal to or greater than $key. If there is no match then returns -1.

WARNING: I intend to change this method so that it accepts a block in the same way that sort does. This means that you will be able to use $a and $b as expected. Until then take care with this one : )

  my $cmp_sub = sub { $_[0] cmp $_[1] };
  my $idx = custom_list_search( $cmp_sub, $key, \@sorted_list );

Searches the list using the subroutine to compare the values. Returns the index of the first entry that is equal to or greater than $key. If there is no match then returns -1.

NOTE - the list must have been sorted using the same comparison, ie:

  my @sorted_list = sort { $cmp_sub->( $a, $b ) } @list;

list_contains, nlist_contains, custom_list_contains

    my $bool =  list_contains( $key, \@sorted_list );   # string sort
    my $bool = nlist_contains( $key, \@sorted_list );   # number sort

    my $bool = custom_list_contains( $cmp_sub_ref, $key, \@sorted_list );

Returns true if $key was found in the list, false otherwise.

AUTHOR

Edmund von der Burg <evdb@ecclestoad.co.uk>

http://www.ecclestoad.co.uk

SEE ALSO

For fast sorting of lists try Sort::Key. For matching on not just the start of the item try Text::Match::FastAlternatives. For matching in an unsorted list try List::MoreUtils.

CREDITS

Sean Woolcock submitted several bug fixes which were included in 0.3

SVN ACCESS

You can access the latest (possibly unstable) code here:

http://dev.ecclestoad.co.uk/svn/cpan/List-Search

COPYRIGHT

Copyright (C) 2007 Edmund von der Burg. All rights reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself. If it breaks you get to keep both pieces.

THERE IS NO WARRANTY.