After all, if it ain't broke, don't fix it. On the other hand, a stitch in time saves nine. On the third hand, a penny saved is a penny earned. Or maybe that was the fourth hand.

The OP has his reasons for asking the question, and as some other commenters have shown, it's a good jumping-off point for discussion of how to reason about different collections of data indexed in different ways. Given that the OP could have written both approaches, benchmarked them, and chosen whichever came out best in about 10 minutes, I don't see "a lot of time" being "wasted."