I suspect that the fastest way is to "add" %hash2 to %hash1 via:     @hash1{keys %hash2}= values %hash2; but this has come up several times before and I'm pretty sure someone has run benchmarks to meet all of your premature nano-optimization needs. (:

Of course, this requires you to define your interface to allow the addition of one "set" to another without having to make a copy. I consider this a good thing. :)

        - tye (but my friends call me "Tye")