in reply to Sorting by the hash value

This is probably what you want to do:

foreach my $key (
               map { $_->[0] }
               sort { $a->[1] <=> $b->[1] }
               map { [$_, $list{$_}] }
               keys %list ) {
...

[download]

See the Schwartzian Transform for more info.

Update: ok.. so I probably must have added the <joke> tags around ;) I figured it would be obvious... since the guy already has a subroutine to sort in. :).

He who asks will be a fool for five minutes, but he who doesn't ask will remain a fool for life.

Chady | http://chady.net/

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Re:x2 Sorting by the hash value
by grinder (Bishop) on Jul 29, 2002 at 06:45 UTC
    Wow! Using a Schwartz Transform to sort a hash by value is like using a sledgehammer to crack open a peanut. The ST is not cheap, it only wins when the cost of computing the key is relatively expensive, and accessing a hash value by key is one of the cheaper things you can do in Perl. I wonder just how much slower this is?

    # /usr/bin/perl -w

use strict;
use Benchmark qw/cmpthese/;

cmpthese( shift || 10_000, {
  'sort'        => sub { sort keys %ENV },
  'sort by key' => sub { sort {$ENV{$a} cmp $ENV{$b}} keys %ENV },
  'sort by ST'  => sub { map { $_->[0] }
                         sort { $a->[1] cmp $b->[1] }
                         map { [$_, $ENV{$_}] } keys %ENV
                     },
});
__END__
% perl -w sortem 100000
Benchmark: timing 100000 iterations of sort, sort by ST, sort by key..
+.
      sort:  2 wallclock secs ( 1.35 usr +  0.00 sys =  1.35 CPU) @ 73
+964.50/s (n=100000)
sort by ST: 18 wallclock secs (17.72 usr +  0.00 sys = 17.72 CPU) @ 56
+44.62/s (n=100000)
sort by key:  2 wallclock secs ( 1.34 usr +  0.00 sys =  1.34 CPU) @ 7
+4515.65/s (n=100000)
               Rate  sort by ST        sort sort by key
sort by ST   5645/s          --        -92%        -92%
sort        73964/s       1210%          --         -1%
sort by key 74516/s       1220%          1%          --

    [download]

    Yep, pretty slow! (I threw the straight sort in there as well, just to give an idea of the overhead incurred by using a sort code block).


    print@_{sort keys %_},$/if%_=split//,'= & *a?b:e\f/h^h!j+n,o@o;r$s-t%t#u'
[reply]
[d/l]
      Wow! Using a Schwartz Transform to sort a hash by value is like using a sledgehammer to crack open a peanut.

      This realization ought to have been the clue that guided you to the true purpose of Chady's node. :)

[reply]

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