Question

I have a seq of seqs in FSharp. I want to join a seq to the previous one if a predicate returns to true for it.

Sample:

let items = seq [seq[2;3;4];seq[1;5;6;7;1;9];seq[2;3;5;7]]

I want to join a seq to the previos one, if the seq starts by 1, so the result should be in this case:

seq [seq[2;3;4;1;5;6;7;1;9];seq[2;3;5;7]]

Is there any nice functional way to do it?

I am just started to translate my long computation processes from C# to F# and very impressed by the performance improvement I could achieve after even a very few hours of work and my beginner level knowledge of FSharp.

I have bought a book from Amazon entitled ‘Beginning F#’. It is really great, but I mainly should work with seqs, lists, maps, collections now and this topic isn’t explained as detailed as I need. Would anyone be so kind to advise me a good resource about ths topics?

Thx in advance!

Answer 1

let joinBy f input =
  let i = ref 0
  input 
  |> Seq.groupBy (fun x ->
    if not (f x) then incr i
    !i)
  |> Seq.map (snd >> Seq.concat)

joinBy (Seq.head >> ((=) 1)) items