1.10: Schwartian Transform (ST) Sort

• Caches extracted keys in an anonymous array for each input record
• Stores the record itself in slot 0 of the array
• Uses the map/sort/map idiom
• Popularized by Randal Schwartz
• Good for medium to large sort sets
• Key extraction is O( N )
• Does a full callback to Perl in the comparison block
• Pass 'ST' option to make_sorter

  sub {
          map $_->[0],
          sort {
          $a->[1] cmp $b->[1]
                  ||
          $a->[2] cmp $b->[2]
  
          }
          map [ $_,
                  do{ my ($val) = $_->[0] ; $val },
                  do{ my ($val) = $_->[1] ; $val }
          ], @_  ;
  }