F# 结合两个序列

Question

我有两个序列，我想以某种方式组合它们，因为我需要将第二个序列的结果打印在第一个序列的旁边。该代码目前是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

如有任何帮助，我们将不胜感激。

Answer 1

正如 Foggy Finder 在评论中所说，在你的具体情况下你真的没有两个序列，你有一个序列并且你想为每个项目打印两行，这可以用一个 Seq.iter 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)

不过，我还会告诉您两种组合两个序列的方法，以防您确实确实有两个不同的序列。首先，如果你想把两个序列变成一个元组序列，你会使用 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)]

如果您想以某种其他方式组合两个序列而不是生成元组，请使用Seq.map2并向其传递一个双参数函数：

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 就是您的朋友：

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

请注意，在 Seq.iter 函数中，我没有存储结果。那是因为 Seq.iter 的结果始终是 ()，"unit" 值相当于 F# 中的 void。（除了它比 void 有用得多之外，原因超出了这个答案的范围。在 Stack Overflow 中搜索“[F#] unit”，你应该会找到一些有趣的问题和答案，比如 this one.

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