Question

I have two sequences (of tuples) on which I need to do a join:

• Seq 1: [(City1 * Pin1), (City2 * Pin2), (City1 * Pin3), (City1 * Pin4)]
• Seq 2: [(Pin1 * ProductA), (Pin2 * ProductB), (Pin1 * ProductC), (Pin2 * ProductA)]

into the sequence (of tuples):

• [(City1 * ProductA), (City2 * ProductB), (City * ProductC), (City2 * Product A)…]

In C# I could do this using the Linq Join extension method like:

seq1.Join(seq2, t => t.Item2, t=> t.Item1,
    (t,u) => Tuple.Create(t.Item1, u.Item2))

How do I accomplish this in F#? I cannot find join on Seq there.

Answer 1

Edit: Actually, you can just use LINQ:

> open System.Linq;;
> let ans = seq1.Join(seq2, (fun t -> snd t), (fun t -> fst t), (fun t u -> (fst t, snd u)));;

---

Why not use F#’s native Seq functions? If you look at the docs and at this question you can simply use these instead of LINQ. Take the Seq.map2 function for example:

> let mapped = Seq.map2 (fun a b -> (fst a, snd b)) seq1 seq2;;

val it : seq<string * string> =
  seq [("city1", "product1"); ("city2", "product2")]

should give you what you want, where seq1 and seq2 are your first and second sequences.