I'd use a Map in GHC 6.4:
count xs = toList $ fromListWith (+) (zip xs (repeat 1))
or a FiniteMap in earlier versions:
count xs = fmToList $ addListToFM_C (+) emptyFM (zip xs (repeat 1))
both of these seem to be quite fast.
- Cale
On 4/28/05, Dmitry Vyal
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.
Any proposals?
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