Hi Aukur kuls,
If I may add my voice to that of others, that what you seek can be done in a single "breath" with what is called popularly known as Schwartzian Transform.
Using a modified version of what you posted one can do:

use warnings;
use strict;

print map { $_->[0] }
      sort { $b->[1] <=> $a->[1] }
      map { [ $_, ( split /[,\s\D]+/, $_ )[2] ] } <DATA>;

__DATA__
field15,field78,filed0 
field90,field12,filed23  
field3,field55,filed67
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