F# 组合两个序列

Question

我有两个序列，我想以某种方式组合它们，因为我需要在第一个序列旁边打印第二个序列的结果。代码当前是 playerItems 引用列表的地方:

seq state.player.playerItems
      |> Seq.map (fun i -> i.name)
      |> Seq.iter (printfn "You have a %s")

seq state.player.playerItems
      |> Seq.map (fun i -> i.description) |> Seq.iter (printfn "Description =  %s")

目前的结果是

You have a Keycard
You have a Hammer
You have a Wrench
You have a Screw
Description =  Swipe to enter
Description =  Thump
Description =  Grab, Twist, Let go, Repeat
Description =  Twisty poke

但是，我需要它

You have a Keycard
Description =  Swipe to enter
You have a Hammer
Description =  Thump

对此的任何帮助将不胜感激。

Answer 1

正如 Foggy Finder 在评论中所说，在您的特定情况下，您确实没有两个序列，您只有一个序列，并且您想为每个项目打印两行，这可以通过一个 Seq.iter 来完成。像这样:

state.player.playerItems  // The "seq" beforehand is not necessary
|> Seq.iter (fun player -> printfn "You have a %s\nDescription = %s" player.name player.description)

但是，我也会告诉您组合两个序列的两种方法，当您确实有两个不同的序列时。首先，如果你想把两个序列变成一个元组序列，你可以使用 Seq.zip :

let colors = Seq.ofList ["red"; "green"; "blue"]
let numbers = Seq.ofList [25; 73; 42]
let pairs = Seq.zip colors numbers
printfn "%A" pairs
// Prints: seq [("red", 25); ("green", 73); ("blue", 42)]

如果您想以其他方式组合两个序列而不是生成元组，请使用 Seq.map2并传递给它一个两个参数的函数:

let colors = Seq.ofList ["red"; "green"; "blue"]
let numbers = Seq.ofList [25; 73; 42]
let combined = Seq.map2 (fun clr num -> sprintf "%s: %d" clr num) colors numbers
printfn "%A" combined
// Prints: seq ["red: 25"; "green: 73"; "blue: 42"]

最后，如果您只想对两个序列中的每对项目执行一些副作用，那么 Seq.iter2是你的 friend :

let colors = Seq.ofList ["red"; "green"; "blue"]
let numbers = Seq.ofList [25; 73; 42]
Seq.iter2 (fun clr num -> printfn "%s: %d" clr num)

这会将以下三行打印到控制台:

red: 25
green: 73
blue: 42

注意如何在 Seq.iter函数，我不存储结果。那是因为 Seq.iter 的结果总是 () ，相当于 F# 的“单位”值 void . (除了它比 void 有用得多，原因超出了本答案的范围。在 Stack Overflow 中搜索“[F#] unit”，您应该会找到一些有趣的问题和答案，例如 this one 。