Here's an example of what hippo was talking about. Note that it only works for positive integers in the range 0 .. 4,294,967,295.

c:\@Work\Perl\monks>perl -wMstrict -le
"use Data::Dump qw(dd);
 ;;
 my @raw_keys = (
   '1    12301    A    B',
   '2    4501    A    B',
   '1    12299    E    F',
   '2    4502    C    D',
   '1    12310    A    B',
   '2    4499    C    D',
   '2    15410    A    B',
   );
 ;;
 my $ornament = 'N N';
 my $decorate   = qq{  $ornament  a*};
 my $undecorate = qq{x[$ornament] a*};
 ;;
 my @sorted_keys =
   map unpack($undecorate),
   sort
   map pack($decorate, (split ' ', $_, 3)[0,1], $_),
   @raw_keys
   ;
 dd \@sorted_keys;
"
[
  "1    12299    E    F",
  "1    12301    A    B",
  "1    12310    A    B",
  "2    4499    C    D",
  "2    4501    A    B",
  "2    4502    C    D",
  "2    15410    A    B",
]
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