I had a go with things along this theme and came up with a couple of
options, with different type signatures. I use some functions from the
Data.List library.
If we know that, as with Ints, we are dealing with list members that are
instances of Ord, we can do:
howManyEqual :: (Eq a, Ord a) => [a] -> Int
howManyEqual = maximum . (0 :) . map length . group . sort
Otherwise, we end up less efficient, with:
howManyEqual :: Eq a => [a] -> Int
howManyEqual = countEach 0
where
countEach best [] = best
countEach best list@(x:_) =
let (xs, others) = partition (== x) list
in countEach (max (length xs) best) others
-- Mark
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