Re: [Haskell-cafe] How to speed things up

Dmitry Vyal wrote:

Hello everybody.

I have a long list consisted of a small number (about a dozen) of elements repeating in random pattern. I know all the possible elements. I need to count number of occurences of each particular element and to do i quickly.

For example quick_func Eq a => [a] -> [(a,Int)] quick_func [1,2,3,1,2,9,1,9] == [(1,3),(2,2),(3,1),(9,2)]

According to profiler this function is the bottle-neck in my sluggish program so I really need to speed it up.

What's been tried so far? Below is a snippet using arrays. You'd probably get a faster program with Unboxed arrays and unsafeAccumArray.

import Data.Array

main = print $ quick_func [1,2,3,1,2,9,1,9]

quick_func is = assocs $ accumArray (+) 0 (1,12) [(i, 1) | i<-is]