Re^2: Sorting Index of An Array

[salva]

Use a Schwartzian transform

To sort lists of nine elements, applying the ST is probably counterproductive. And anyway, for that particular problem, using a Orcish Maneuver would be more suitable:

my @index_sorted = map {
  my @row = splice @sim, 0, N;
  sort { $row[$b] <=> $row[$a] } 0..(N-1);
} 0..(M-1);

[shmem]

Just a nit - while your approach is far better than mine and less convoluted, there's no OR and no cache, so there's no Orcish (or-cache) Maneuver. That would be (from Shlomo Yona's Perl lectures 2002):

The Orcish Maneuver -- example

keys my %or_cache = @in;
@out = sort {
    ($or_cache{$a} ||= KEY($a))
    cmp
    ($or_cache{$b} ||= KEY($b))
} @in;

The first part of the sortsub sees if the sortkey for $a is cached.

If not, it extracts the value of the sortkey from the operand and caches it.

The sortkey for $a is then compared to the sortkey for $b.

Anyways, salva++ for simplifying things :-)