On Tue, 28 Dec 2010, Robert Clausecker wrote:
Hi folks!
I have the following problem. As code is most time easier to understand,
let give an example what I try to do in C:
unsigned int i,j;
unsigned int r[100];
for (i = 0; i < 1000000; i++) {
j = makeResult(); //j is known to be smaller than 100.
r[j] = r[j] + 1;
}
(My C is poor, so please don't laugh)
Currently I'm using a Data.Map for this, but as the result is bounded in
this area, an array seems to be more appropreate. I don't want to mess
with mutable arrays, but I can't find anything which does the same like
Data.Map.insertWith for arrays in a reasonable way.
Mutable arrays in ST monad sound like a reasonable choice.
In my example, the input comes from a lazy list and is than folded into
the Map by insertWith (+) j 1 r. Is there any nice, quick way to do this
with Arrays without using mutable ones?
You may attach a one to the list elements and then call Array.accum with
(+). The corresponding function in Data.Map is Data.Map.fromListWith with
(+).
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