In F# at some point I have many lists (the actual number of them differs for input data) and I want to make an aggregation over all those lists (let say addition for simplification). So what I want to achieve is the same what List.map2 or List.map3 does but for bigger number of lists.
How can I approach it? I was wondering if this is possible to do with List.scan?
You can use List.reduce and do something like this:
> let lists = [[1;2;3]; [1;2;3]; [1;2;3]]
val lists : int list list = (...)
> lists |> List.reduce (List.map2 (+));;
val it : int list = [3; 6; 9]
What does this do?
List.reduce takes a list of values (here the value is int list) and it aggregates them into a single value using a function that says how to merge two values. So in this case, we need to give it a function int list -> int list -> int list and it will call it on the first and the second list, then on the result and the third list (and so on).
The argument List.map2 (+) is a function of the right type - it takes two lists and performs pairwise sum of the two lists. This is really just a shortcut for writing something like:
lists |> List.reduce (fun list1 list2 ->
List.map2 (fun a b -> a + b) list1 list2)
