Getting every nth Element of a Sequence
- by Alexander Rautenberg
I am looking for a way to create a sequence consisting of every nth element of another sequence, but don't seem to find a way to do that in an elegant way. I can of course hack something, but I wonder if there is a library function that I'm not seeing.
The sequence functions whose names end in -i seem to be quite good for the purpose of figuring out when an element is the nth one or (multiple of n)th one, but I can only see iteri and mapi, none of which really lends itself to the task.
Example:
let someseq = [1;2;3;4;5;6]
let partial = Seq.magicfunction 3 someseq
Then partial should be [3;6]. Is there anything like it out there?
Edit:
If I am not quite as ambitious and allow for the n to be constant/known, then I've just found that the following should work:
let rec thirds lst =
match lst with
| (_,_,x)::t -> x::thirds t
| _ -> []
Would there be a way to write this shorter?
