Return value given a key

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi, Below is a piece of code that reads from a file and builds a hash:


#!/usr/bin/perl
%Test_hash=();

open(F, "xfile.test");
while ($line=<F>){
      if ($line=~ /FIRST/) {
          ($Test_num,$Test)=(split(/\s+/,$line))[0,2];
          push (@Tests,$Test);
           @all_me=();
        }
          if ($line=~ /SUBSET/ ) {
              $me=(split(/\s+/,$line))[2];
              push(@all_me,$me);
              $Test_hash{$Test} = [@all_me];
}

}

use Data::Dumper;
print Dumper([\%Test_hash]);

__DATA__

<xfile.test>

FIRST      ONE     TEST1

SUBSET        a.me

SUBSET          b.me

SUBSET          c.me
[download]

The hash is something like TEST1 (key) - all *.me's as values. I am looking at passing *.me as an argument and it should return the corresponding key. HELP!!??? Thanks

Comment on Return value given a key Download Code

Replies are listed 'Best First'.
Re: Return value given a key by Perl Mouse (Chaplain) on Nov 22, 2005 at 11:20 UTC
You title suggest you have a key, and want a value, but your question is actually the other way around. The answer is that if you want to find a key belonging to a certain value, you should have used a different datastructure. In a hash, keys are unique, values don't have to. The entire point of a hash is to be able to search with keys - if you want to search with the values, you should have used the values as the keys, and the keys as the values. `Perl --((8:>*`	[reply]
Re^2: Return value given a key by monarch (Priest) on Nov 22, 2005 at 13:01 UTC
Or, if you want to speed up looking for a value, build an inverse hash.. `my %forwardhash = ( key1 => 'value1', key2 => 'value2', key3 => 'value3' ); my %reversehash = (); while ( my ( $key, $value ) = each %forwardhash ) { $reversehash{$value} = $key; } use Data::Dumper; print Dumper( \%reversehash );` [download] Outputs: `$VAR1 = { 'value1' => 'key1', 'value2' => 'key2', 'value3' => 'key3' };` [download]	[reply] [d/l] [select]