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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??


in reply to Re: How to get Keys from hash having same value?
in thread How to get Keys from hash having same value?

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.


Comment on Re^2: How to get Keys from hash having same value?
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Re^3: How to get Keys from hash having same value?
by shmem (Canon) 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

    Ah well. Readability... ;-)

    --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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