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

by Thilosophy (Curate)
 on Jan 07, 2008 at 07:32 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.

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Re^3: How to get Keys from hash having same value?
by shmem (Chancellor) on Jan 07, 2008 at 14:19 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 13:22 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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