This is what the original poster did, but with different variable names and a slightly different regex, and it ran out of memory. But isn't this O(N2)? It seems to me that it greps every item in one array against all the items in the other array, so it's really no different from this: 

my @array3;
OUTER:
for my $a1 (@array1){
  for my $a2 (@array2){
    next OUTER if they_match_somehow();
  }
  push @array3, $a1;  # it didn't match anything in @array2
}

[download]

Both cases have two nested loops; it's just harder to see them in the grep-within-a-grep method.

Aaron B.
Available for small or large Perl jobs; see my home node.

In reply to Re^4: Memory issue with large array comparison by aaron_baugher
in thread Memory issue with large array comparison by bholcomb86

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