Felipe, On Thu, Aug 12, 2010 at 9:23 PM, Felipe Lessa wrote:

On Thu, Aug 12, 2010 at 10:11 PM, Patrick LeBoutillier wrote:

...

I need a function that, given t and the list of t*m measures, can spilt the measures by track, returning a list of t lists, each containing m measures. I cannot figure out how to do this, even though it seems to me like it shouldn't be too hard... I can't figure out how to "update" the lists of lists when I want to add a new element.

Do anyone have any ideas?

I won't post the complete code and will just throw ideas around, please let us know if you still get stuck =).

Perfect!

We have the following function in the Prelude:

 splitAt :: Int -> [a] -> ([a], [a])

For example,

 Prelude> splitAt 3 [1..12]  ([1,2,3],[4,5,6,7,8,9,10,11,12])

So you can write the following function (you can choose another name):

 separate :: Int -> [a] -> [[a]]

For example,

 Prelude> separate 3 [1..12]  [[1,2,3],[4,5,6],[7,8,9],[10,11,12]]

But that's not what we wanted.  Hmmm, from Data.List we have

 transpose :: [[a]] -> [[a]]

For example:

 Prelude Data.List> transpose [[1,2,3],[4,5,6],[7,8,9],[10,11,12]]  [[1,4,7,10],[2,5,8,11],[3,6,9,12]]

Bingo!

Hope that helps ;-),

Yes, that's exactly what I was looking for! Thanks, Patrick

-- Felipe.

-- ===================== Patrick LeBoutillier Rosemère, Québec, Canada