Ooops!

syntax error at /tmp/615254.pl line 41, near "N
    push"
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After some correction (and addition to print out the sorted array), here is the result:

0   1   3   2   4   5   7   8   6
1   0   3   8   2   4   7   6   5
2   3   8   0   1   4   7   5   6
3   0   1   2   8   7   6   4   5
4   8   7   0   1   2   6   3   5
5   0   7   1   2   3   6   8   4
6   7   8   3   4   1   2   0   5
7   6   8   3   4   0   1   5   2
8   7   6   3   4   1   2   0   5
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This orcish manuever is really new to me. And I'm tempted to benchmark these two techniques. Here it goes:

#!/usr/bin/perl

use strict;
use warnings;

my @sim_st = qw(
    1.0    0.9    0.3    0.6    0.3    0.3    0.2    0.3    0.3
    0.9    1.0    0.3    0.5    0.3    0.1    0.2    0.3    0.4
    0.3    0.3    1.0    0.6    0.3    0.2    0.2    0.3    0.4
    0.6    0.6    0.6    1.0    0.2    0.2    0.3    0.4    0.5
    0.3    0.3    0.3    0.2    1.0    0.1    0.3    0.4    0.5
    0.3    0.2    0.2    0.2    0.1    1.0    0.2    0.3    0.2
    0.1    0.2    0.2    0.3    0.3    0.1    1.0    0.8    0.6
    0.3    0.3    0.2    0.4    0.4    0.3    0.8    1.0    0.8
    0.3    0.4    0.4    0.5    0.5    0.2    0.6    0.8    1.0
);

my @sim_om = @sim_st;

use Benchmark 'cmpthese';

my $count = shift || -1;
cmpthese $count, {
    sort_with_st => \&sort_st,
    sort_with_om => \&sort_om,
};

sub sort_st {
    my @sim = @sim_st;
    my @sorted =
       map { $_->[0] }
          map {
            my $i = 0;
            sort { $b->[1] <=> $a->[1] }
                 map { [$i++, $_] } splice (@sim, 0, 9)
         }
         0..8;
}

use constant { M => 9, N => 9 };
sub sort_om {
   my @index_sorted;
   for my $m (0..(M-1)) {
      my $ix0 = $m * N;
      push @index_sorted,
           sort { $sim_om[$ix0 + $b] <=> $sim_om[$ix0 + $a] }
                0..(N-1);
   }
}
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And here is the benchmark, kinda speaks for itself:

$ perl benchmark-sort.pl
               Rate sort_with_st sort_with_om
sort_with_st 3011/s           --         -61%
sort_with_om 7724/s         156%           --
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Thanks and ++ goes to shmem and salva for the lessons.