Re: sort after first char of hash key

[Cristoforo]

Here is the Guttman-Rosler Transform.

#!/usr/bin/perl
use strict;
use warnings;
use 5.012;
use List::Util qw/ shuffle /;

srand(1); # to get same random 'shuffle' from run to run
my @list = shuffle (qw/ Y2 A15 YABBA287 DABBA345 DOO777/, map {"E$_"} 
+(1..20));

say "UNSORTED";
say "@list";

my @sorted = map { 
                   my $strlength = unpack("C", substr($_, -1));
                   substr $_, -1 * (1 + $strlength), -1;
                 }
            sort
             map { pack "a*Na*C", /(\D+)(\d+)/, $_, length} @list;

say "SORTED";
say "@sorted";

The advantage of this sort is that it uses a simple alphabetical sort. Its is usually the fastest performing sort. The configuration here will sort any 'alpha'+'number' string, not just a single leading letter plus a number.

Update: The setup here is limited to strings of length <= 255. If the strings to be sorted are longer than that, you would have to make some changes. Also, to make the sort case insensitive, which is usually the desired outcome, the first map could be restated as:

map { pack "a*Na*C", (map {lc} /(\D+)(\d+)/), $_, length} @list;

by adding the lc operator.