where_not_in (Solved)

[eluser]jedd[/eluser]
Did you try using array_diff()?

I'm assuming that Array2 is, always, a superset of Array1 in this instance?

Array messing usually provides much scope for confusion - I always end up writing a test function with a fair bit of data to confirm it's really doing what it's promising to do. Not sure if the arrays need to be sorted prior to hand-over to array_diff(), or if it does an exhaustive loop-within-a-loop (I'd imagine the latter).