"It works a treat, but I cannot for the life of me wrap my head around how and why, and I hate using code I can't understand (for several reasons)."

Firstly, I'm glad to hear you're not just blindly plugging in code you don't understand.

The "map {} sort {} map {}" construct is known as the "Schwartzian Transform" (to which Laurent_R referred earlier in this thread).

Where you encounter combinations of functions which take a list and return a list (e.g. grep, map, sort, etc.), it's often best to evaluate them in reverse order.

Consider this (clunky) rewrite of that piece of code:

my @indices_of_myhash_key_info_array
    = 0 .. $#{$myHash{$key}{info}};

my @two_element_arrayrefs_with_sortkey_and_data
    = map {
        [ split /:/, $myHash{$key}{info}[$_], 2 ] 
    } @indices_of_myhash_key_info_array;

my @two_element_arrayrefs_sorted_by_sortkey
    = sort {
        $a->[0] <=> $b->[0]
    } @two_element_arrayrefs_with_sortkey_and_data;

my @data_element_only_sorted_by_sortkey
    = map {
        $_->[1] 
    } @two_element_arrayrefs_sorted_by_sortkey;

for (@data_element_only_sorted_by_sortkey) {
    print "$_,$key";
}
[download]

Hopefully that explains what is going on but feel free to ask if anything needs further explanation.