I don't know what this tuple is representing, but if you want to group you'll have to specify on 'what': - the tuple, - the fst or - the snd Here's a possibility with grouping on the fst import Data.List import Data.Ord import Data.Function groupAtoms :: (Float -> Bool) -> [(Float,Integer)] -> ([[(Float,Integer)]],[[(Float,Integer)]]) groupAtoms p = partition (p.sum. map fst). groupBy ((==)`on`fst). sortBy (comparing fst) Use: groupAtoms (>=1.0) myList If this is what you want: proper lists are in the fst of the result. Hallo João Paulo Pizani Flor, je schreef op 23-11-10 18:23:

Hello dear Haskellers!

I've been a user and big fan of Haskell for a while, but only now I'm writing my first "big" project in Haskell (some thousands of lines of code perhaps). It's an interpreter for a programming language, the source code is music! Yes, sheet music! :D

OK, so my specific problem goes like this: I have a list of tuples :t myList [ (Float, Integer) ]

And I want to "group" this list into a nested list groupAtoms :: [ (Float,Integer) ] -> [ [(Float,Integer)] ]

Of course, I want that the concatenation of the groups yield me the original list, i.e, (foldl (++) [] . groupAtoms == id), and the criterion that defines a group is that: "The sum of the first elements in the tuples comprising the list must be greater than or equal to 1.0". That is, given a list of tuples, the boolean predicate deciding whether this list is a PROPER group (True) or TOO SMALL (False) is: \g -> sum (map fst g) >= 1.0

Although the criterion is very clear, I've tried hard until now and couldn't come up with a function for producing the nested list based on this grouping criterion. I am sure that the Haskell Hierarchical Libraries have something to help me, but only now I see I'm still a big noob :P

Could someone please help me writing this function?

My best regards from Brazil,

João Paulo Pizani Flor joaopizani@gmail.com mailto:joaopizani@gmail.com Federal University of Santa Catarina

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