I could use some guidance on the best way to tackle a somewhat complex sorting problem I need to work though. I will try to keep this as generic as possible.

I have to grab 4 numbers from every line in a file. Each line is formatted in a very predictable pattern. Say I name each number like so:-

$row_lx
$row_ly
$row_ux
$row_uy

NOTE: Many of the $row_lx values will be the same.
NOTE: MOST of the $row_ly values will be different.

Here is a nice, neat, golden output. Imagine all of the following lines were originally completely out of order:-

((1.0 0.1) (99.0 0.2))
((1.0 0.2) (99.0 0.3))
((1.0 0.3) (99.0 0.4))
((5.0 0.4) (48.0 0.5))
((48.1 0.4) (99.0 0.5))
((1.0 0.5) (99.0 0.6))
((1.0 0.6) (13.0 0.7))
((13.1 0.6) (99.0 0.7))

Notice that the second number (highest priority), $row_ly, always increases, and sometimes it is repeated. When it does repeat, always print the $row_lx numbers in order (second priority).

I hope this is clear enough. Any recommendations? I think I need a hash with two primary key values, but I don't know how to sort the hash to produce the above output.

Thanks,
-Anonymous Monk #N