如何调用Enumerable。从f_加入?

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

Seq at the docs at this question Seq.map2

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

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

seq1 seq2

> let seq1 = seq [("city1", "pin1"); ("city2", "pin2")];;

val seq1 : seq<string * string> = [("city1", "pin1"); ("city2", "pin2")]

> let seq2 = seq [("pin1", "product1"); ("pin2", "product2")];;

val seq2 : seq<string * string> = [("pin1", "product1"); ("pin2", "product2")]

> Seq.zip seq1 seq2;;
val it : seq<(string * string) * (string * string)> =
  seq
    [(("city1", "pin1"), ("pin1", "product1"));
     (("city2", "pin2"), ("pin2", "product2"))]
> Seq.zip seq1 seq2 |> Seq.map (fun (x,y) -> (fst x, snd y));;
val it : seq<string * string> =
  seq [("city1", "product1"); ("city2", "product2")]

open System.Linq

open System

let seq1 = seq [("city1", "pin1"); ("city2", "pin2"); ("city1", "pin3"); ("city1", "pin4")]
let seq2 = seq [("pin1", "product1"); ("pin2", "product2"); ("pin1", "product3"); ("pin2", "product1")]

let joinSeq = seq { for x in seq1 do
                        for y in seq2 do
                            let city, pin = x
                            let pin1, product = y
                            if pin = pin1 then
                                yield(city, product) }
for(x,y)in joinSeq do
    printfn "%s: %s" x y

Console.ReadKey() |> ignore

• List.zip List.map2

  Join Zip

• seq { for city, pin1 in seq1 do 
          for pin2, product in seq2 do 
            if pin1 = pin2 then yield city, product }
  

  seq2 seq1 O(seq1.Length * seq2.Length)

  open System.Linq
  module Seq = 
    let join (seq1:seq<_>) seq2 k1 k2 =
      seq1.Join(seq2, (fun t -> k1 t), (fun t -> k2 t), (fun t u -> t, u)) 
  

  (seq1, seq2) 
     ||> Seq.join snd fst 
     |> Seq.map (fun (t, u) -> fst t, snd u)
  

zip join