Laziness is not free. An eager loop will be faster than a lazy construct, especially languages where the laziness isn't really a first class construct. Like ruby.

Rewriting the code you wrote (or was it the other guy? I am making food so I cant really check) to avoid intermediate collections as a for loop will be faster, especially if you can avoid creating those array pairs.

I am not saying ruby stinks. I am saying it - and just about every other language - is making it unnecessarily hard to write fast code.