I'm a newbie here, so I'm not sure about my reply, but I think this is
not the answer to his question.
freq ["egg", "egg", "cheese"] indeed returns [2,1]
but
freq ["egg", "cheese", "egg"] returns [1,1,1]
BH just mentioned he needed the frequenty of elements in the list,
independent of their order.
So in that case, the result should be a list of ordered pairs like:
[("egg", 2), ("cheese", 1)]. Or a pair of two lists, like (["egg",
"cheese"), (2,1)]. Otherwise you would not know which frequency belongs
to which element?
I can't write this concisely nor efficient yet, but the following does
the job:
import Data.List
freq xs = zip e f
where
s = sort xs
e = nub s
f = map length (group s)
However, I suspect the experts here will be able to make that much
shorter and more efficient (maybe using Data.Map?)
Peter
Stefan Holdermans wrote:
BH,
Is there a library function to take a list of Strings and return a
list of
ints showing how many times each String occurs in the list.
So for example:
["egg", "egg", "cheese"] would return [2,1]
freq xs = map length (group xs)
HTH,
Stefan
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