in reply to Returning indices with same values for array within hash.

All solutions so far have two passes over the array, but it can be done in one as well. I am using each, so you need one of the newer Perls. 

use strict;
use warnings;

my %matrix = (NI => [2, 1 ,1 ,3 ,4] );
my @NI_index;
my $min;
while( my ($i, $v) = each @{$matrix{NI}} ) {
    if( not defined $min or $v < $min ) {
        $min = $v;          # found new minimum
        @NI_index = ();     # empty list
    }
    push @NI_index, $i if $v == $min;
}
print "@NI_index\n";

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Re^2: Returning indices with same values for array within hash.
by AnomalousMonk (Archbishop) on Nov 11, 2013 at 17:12 UTC
    ... each ... newer Perl ...

    Perl version 5.12+, and 5.14+ has the "highly experimental" feature of allowing each to directly take a reference: 

    >perl -wMstrict -le
"my %matrix = (NI => [2, 1, 1, 3, 4] );
 ;;
 my @NI_index;
 my $min;
 while (my ($i, $v) = each $matrix{NI}) {
   if(not defined $min or $v < $min) {
     $min = $v;
     @NI_index = ();
     }
   push @NI_index, $i if $v == $min;
   }
 print qq{@NI_index};
"
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