On 3/3/11 7:18 PM, Jacek Generowicz wrote:
Hi Cafe,
It seems that I don't understand what groupBy does.
I expect it to group together elements as long as adjacent ones satisfy the predicate, so I would expect ALL four of the following to give one group of 3 and a group of 1.
Prelude> :m + Data.List Prelude Data.List> groupBy (<) "abcb" ["abcb"] Prelude Data.List> groupBy (<) "abca" ["abc","a"] Prelude Data.List> groupBy (<) [1,2,3,2] [[1,2,3,2]] Prelude Data.List> groupBy (<) [1,2,3,1] [[1,2,3],[1]]
What am I missing?
The behavior is that it's comparing subsequent elements to the first element of the current chunk. I'm not sure how often that'd be a desirable behavior compared to the one you and I would expect. Of course, the API only specifies the behavior of groupBy on equality-like predicates IIRC. So technically either behavior is permissible... This should be FAQed on the documentation a bit better. -- Live well, ~wren