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Re: Finding a hash key from the value (reverse lookup)

by kilinrax (Deacon)
on Jan 22, 2001 at 18:36 UTC ( [id://53493]=note: print w/replies, xml ) Need Help??


in reply to Finding a hash key from the value (reverse lookup)

You could always use 'reverse': 
#!/usr/bin/perl -w

use strict;

my %fruit = ( apple => 'green',
              orange => 'orange',
              banana => 'yellow' );

print ${{reverse %fruit}}{'yellow'};

[download]

Replies are listed 'Best First'.
Re: Re: Finding a hash key from the value (reverse lookup)
by PsychoSpunk (Hermit) on Jan 22, 2001 at 23:34 UTC
    You couldn't always use reverse.

    The question asked about non-unique values, thus you end up losing keys that are appropriate values. In this situation, you do not have a 1-1 function so reverse is very bad.

    ALL HAIL BRAK!!!

[reply]

      Well, building a useful reverse index in cases where you don't have a 1:1 mapping isn't too bad (although not as elegant):

      (given %index)

      my %revindex;
for my $revpair (map {
  [ $index{$_}, $_ ]
} keys(%index)) {
  push @{$revindex{$revpair->[0]}}, $revpair->[1];
}

      [download]

      There are probably simpler ways to do even that, however.

[reply]
[d/l]
[reply]

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