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### Re^2: How to get Keys from hash having same value?

by Thilosophy (Curate)
 on Jan 07, 2008 at 02:32 UTC ( #660774=note: print w/replies, xml ) Need Help??

Or, to avoid the extra hash lookups, iterate over key-value pairs using each.
```my @as = ();
while (my (\$key, \$value) = each %myhash){
push @as, \$key if \$value eq 'a';
}

Update:

Is there a monk among us who can shorten this into a one-liner, similar to the grep keys examples we have seen?

It seems that each does not combine nicely with grep, map and their ilk.

Replies are listed 'Best First'.
Re^3: How to get Keys from hash having same value?
by shmem (Chancellor) on Jan 07, 2008 at 09:19 UTC
Voilà:
```%newhash = reverse do { my \$hash = reverse %myhash; %hash };

To get the keys only (which are the values in the reversed hash:

```@unique_keys = do { my \$hash = reverse %myhash; values %hash };

update: oops, got it all wrong. It' about getting all keys where duplicate values are found. As a single statement, formatted for readability

```%myhash = (1 => 'a', 2=> 'b', 3=> 'a', 4=>'c',5 => 'b', 6 => 'a');
@k = do {
my %s;
map {
my \$v=\$_;
grep { \$myhash{\$_} eq \$v} keys %myhash
} grep {\$s{\$_}++==1} values %myhash
};
print "\$_ => \$myhash{\$_}\n" for @k;
__END__
6 => a
1 => a
3 => a
2 => b
5 => b

--shmem

```_(\$_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
/\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.(\$e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;\$e.e && print}```
Re^3: How to get Keys from hash having same value?
by targetsmart (Curate) on Jun 03, 2008 at 09:22 UTC
I tried doing that, It is working.
```use Data::Dumper;
%myhash = ( 1 => 'a', 2=> 'b', 3=> 'a', 4=>'c', 5 => 'a', 6 => 'a', 7
+=>'b');
%newhash = map { (\$_,\$myhash{\$_}) }  grep { \$myhash{\$_} eq 'a'; } keys
+ %myhash ;
print Dumper \%newhash;

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