Obtaining elements at n to n+x in a sequence in fsharp

Question

Quite simply, given a sequence in F#, how does one obtain elements from index n to index n+x (inclusive)?

So, if I have a sequence like: {0; 1; 2; 3; 4; 5}, how to I get the sub-sequence from index 2 to 4? It would look like {2; 3; 4}

Any answer that uses the massive built-in F# API is preferable.

Massimiliano · Accepted Answer · 2012-05-07T03:22:58.077

5

Something like this?

let slice n x = Seq.skip n >> Seq.take (x+1)

Note that if there is not enough elements in the sequence you will get an InvalidOperationException.

edited May 07 '12 at 03:22

answered May 06 '12 at 03:30

Massimiliano

Something exactly like that! I don't know how I missed the "skip" function. Thanks! – MirroredFate May 06 '12 at 03:45
It's generally good style to put the sequence parameter as the last one, so it can be used naturally with the `|>` operator. – yamen May 06 '12 at 07:24
1

You don't need `s`, actually: `let slice start length = Seq.skip start >> Seq.take length` – Be Brave Be Like Ukraine May 06 '12 at 22:29

score 2 · Answer 2 · answered May 06 '12 at 10:09

let slice n x xs =
    xs
    |> Seq.windowed (x + 1)
    |> Seq.nth n

Note that unlike Yacoder's answer, it returns an array instead of a sequence (which may be want you want or not, depending on the situation).

I added my answer to show Seq.windowed, a very useful function IMHO. Seq.pairwise is also nice and good to know about.

2 Answers2