Re: question for perl book & magazine authors

[sauoq]

I'm convinced that map & grep aren't as heavily used as they could be because people don't understand them.

I don't think I agree with the implied premise that map() and grep() should be used more heavily. I'd say they are probably used inappropriately at least as often as appropriate uses for them are missed.

For instance, in the example you gave, you'd probably be better off using a hash to determine common elements.

Update: You should also be more careful to check your benchmarks for correctness. Your "using grep" benchmark doesn't even reference @array1...

Update 2: I also just noticed you are using grep in a scalar context in the unless clause in your "using foreach" sub. That's one of those inappropriate uses of grep I mentioned above...

[holli]

The hash trick is a nice way if the array is small enough. for huge arrays the algorhitmical/runtime trade may be worth the price to save memory.

[sauoq]

Sure... if memory is so tight that you have to choose an O(n * m) time complexity over O(n + m) then I guess you gotta do what you gotta do.

Of course, in that case (and especially if this is a routine task) you are almost certainly going to win by throwing more RAM at the problem because the larger your dataset the more (time) you are saving with the linear algorithm.

Update: Also note that the additional memory you need will be relative to the smaller of your two arrays. (As a possible optimization depending, of course, on your data.)