Corion,
There is at least 1 problem with this code (and possibly 2).

if (!$seen{$name1[$i]}) {

should be

if ( ! $seen{$name1[$i]}++ ) {
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Without the post-increment, everything would be pushed to the unique array. The second possible problem is one of interpretation. I read the original post to mean that there would be some unique entries in a list containing duplicates and the object was to find the first one. If that interpretation is correct - then you have to wait until after going through the first array in its entirety before you can know if an item is unique or not.