Combining a column of lists in OCaml

Question

I want to essentially transpose a matrix in OCaml (without using recursion or any sort of looping)

For example, if I have the following matrix: [[1;2];[3;4]]

Answer 1

I question whether your separate function separates the matrix into columns. Here's what I see:

# let separate li = List.map (fun x -> [x]) li;;
val separate : 'a list -> 'a list list = 
# List.map separate [[1;2];[3;4]];;
- : int list list list = [[[1]; [2]]; [[3]; [4]]]

I don't see columns, I just see that you've put each matrix element into its own list.

To get the first column you could try this:

# List.map List.hd [[1;2]; [3;4]];;
- : int list = [1; 3]

If you use List.tl rather than List.hd you get the remainders of the rows. Maybe you can use a fold to apply this repeatedly and collect up the results.