On Mon, 2011-06-06 at 21:43 -0400, Tom Murphy wrote:
Hi All, This seems like an inefficient way to do what I'm trying to do.
Intuition tells me it's inefficient, but on second thought: You're trying to accumulate (and add) values for a matching given index (in this case, the second argument of the tuple -- btw flipAssoc is available as Data.Tuple.swap). That necessarily means traversing the list, the whole time retaining quick random access to update the value associated with a particular index -- which is exactly what Maps are for, right? The code does exactly what you want with the least complexity, AFAICS, though of course it'd be nicer if there wasn't this List->Map->List. I'd argue this isn't inefficient to do what you're doing, but I'd look for a more general optimisation in the context this code comes from in order to avoid such an operation from the start entirely. :) That may involve keeping a single map, and updating it progressively as each pair comes in (which you can do for the initial creation too, with a fold). Cheers, Arlen