Suppose you have %hash, and you want to show all the keys that share the same given value. %revhash = reverse %hash won't work because of the value collision. Solution: use arrayrefs for values during the inversion!
my %revhash;
while (my ($key, $value) = each %hash) {
  push @{$revhash{$value}}, $key;
}
for (sort keys %revhash) {
  print "$_ => @{$revhash{$_}}\n";
}

[download]
(Revised per mdillon's note, but in a different way for speed)

Replies are listed 'Best First'.
RE: Inverting a hash to get all keys for this value
by mdillon (Priest) on Oct 09, 2000 at 21:11 UTC
    i think you meant this: 
    my %revhash;

push @{$revhash{$hash{$_}}}, $_ for keys %hash;

for (sort keys %revhash)
{
    print "$_ => @{$revhash{$_}}\n";
}

    [download]
[reply]
[d/l]
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