Add group function

Matrix.hs

@@ -19,6 +19,11 @@ xs     ?? n | n < 0 =  Nothing
 (x:_)  ?? 0         =  Just x
 (_:xs) ?? n         =  xs ?? (n-1)
 
+-- | Split a list into sublists of length n
+-- group 2 [1..5] == [[1,2],[3,4],[5]]
+group _ [] = []
+group n xs = take n xs : group n (drop n xs)
+
 -- | Create a matrix of indeces of a matrix
 indeces :: Mat a -> Mat Pos
 indeces (Mat m) = Mat [[(x,y) | y <- [0..length (m !! x)-1]] |