I'm new to haskell and would like some ideas on how to create a function that would take every head element of multilist's lists and add it to a new multilist, then move on to second column and etc.. So far I only know how to write a function for the first column: inverted (xss) = map head xss How to make it to go until it does it with every column of a multilist?

CodePudding user response：

We can write this function directly, and you've got the exact right idea to start with. Get the heads first, and then make a recursive call.

Assuming all of the lists are of the same length,

inverted :: [[a]] -> [[a]]
inverted [] = [] -- Degenerate case
inverted xss
  | null (head xss) = []
  | otherwise = map head xss : inverted (map tail xss)

As it happens, this function is already in the standard library: it's called Data.List.transpose and it does exactly what you want.