Get the Key corresponding to any given value

[rmalhotra]

Is there any way to get the key corresponding to a given value from a hash table

Originally posted as a Categorized Question.

[jsprat]

If the values are unique:

my %rhash = reverse %hash;
my $key = $rhash{$value};

will give you the key for a given value.

If you might have duplicate values, grep is your friend:

my @keys = grep { $hash{$_} eq $value } keys %hash;

If your values are numeric, use "==" instead of eq.

[manav]

Most of these cases have been covered in the perlfaq itself. See How do I look up a hash element by value?

[codeacrobat]

%h=(1 => 2,
    3 => 2,
    4 => 3);

$val = 2;

# use eq for strings, or whatever equals method for objects
@keys = grep {$h{$_} == $val} keys %h; # (1,3)

Originally posted as a Categorized Answer.

[simmisam]

my ($key) = grep {$value ~~ $hash{$_}} keys %hash;
print "Key = $key\n";

[LanX]

values are not necessarily unique so the left hand side should be a list.

and using smart match doesn't make sense, better decide if == or eq are appropriate.

simmisam did you notice that most of your recent answers in this category were rejected by QandAEditors b/c of poor quality?

And (sadly) I have to say, I hope this one too!

Maybe you should stop playing this game till you are more experienced?

[jdporter]

I'm actually OK with this one, but I would prefer that he would include an explanation of the value of his approach, i.e. describe the situations in which he thinks it could be useful.