Sorting your array of arrays, based on your answers on previous questions, demonstrated under the perl debugger:

  DB<2> @c = ([ PF12951, 421, 455 ], [ PF03797, 822, 1073 ], [ PF12951
+, 515, 547 ]);

  DB<3> x @c
0  ARRAY(0x80359d28)
   0  'PF12951'
   1  421
   2  455
1  ARRAY(0x803601b8)
   0  'PF03797'
   1  822
   2  1073
2  ARRAY(0x803603b0)
   0  'PF12951'
   1  515
   2  547
  DB<4> @d = sort {$a->[1] <=> $b->[1]} @c

  DB<5> x @d
0  ARRAY(0x80359d28)
   0  'PF12951'
   1  421
   2  455
1  ARRAY(0x803603b0)
   0  'PF12951'
   1  515
   2  547
2  ARRAY(0x803601b8)
   0  'PF03797'
   1  822
   2  1073
  DB<6>
[download]

Once the sub-arrays are sorted, it is quite easy to pick up the end of the previous element.