Given the simplicity and regularity of your ranges, you could simply compute indices of a two-dimensional array instead, like this: 
use strict;
use POSIX qw(floor);

my $input = $ARGV[0];
open(FILE, $input) || die "ERROR: Unable to open $input FILE for readi
+ng: $!\n";

my @range2;

my ($phi, $psi);
while (<FILE>) {
   $phi = substr($_, 0, 6);
   $psi = substr($_, 8, 6);

   print "$phi $psi\n";
   my $i = floor($phi/5.0) + 36;
   my $j = floor($psi/5.0) + 36;
   if ($i >= 0 && $j >= 0 && $i < 73 && $j < 73) {
      ++$range2[$i][$j];
   }
}

for my $i (0..72) {
   for my $j (0..72) {
      my $val = $range2[$i][$j];
      $val ||= 0;
      print "$val, ";
   }
   print "\n";
}

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In reply to Re: inefficient code? works on small files ok but not larger ones by tall_man
in thread inefficient code? works on small files ok but not larger ones by Anonymous Monk

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