Question

我想在前两个值的集合中找到元组并返回元组的第三个值（如果没有找到则返回None）。我喜欢这样的事情：

type Point = (int * int * int)
type Path = Set<Point>

let f (x:int) (y:int) (p:Path) : int Option =
    if Set.exists ((=) (x, y, _z)) p
    then Some _z
    else None

let p:Path = Set.ofList [ (0, 1, 100); (1, 1, 500); (1, 2, 50); ]

f 1 2 p

但这不起作用，因为显然，表达式中不允许使用模式匹配。什么是正确的方法？感谢。

Answer 1

您可以将设置转换为列表并使用List.tryFind

 <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="android:colorPrimary">@color/colorPrimary</item>
    <item name="android:colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="android:colorAccent">@color/colorPrimary</item>
    <item name="android:windowActionModeOverlay">true</item>
    <item name="android:windowContentTransitions">true</item>
    <item name="android:windowNoTitle">true</item>
    <item name="android:actionModeBackground">@color/colorPrimary</item>
    <item name="android:windowContentOverlay">@null</item>
    <item name="android:textColor">@color/myTextPrimaryColor</item>
    <item name="android:windowAllowEnterTransitionOverlap">true</item>
    <item name="android:windowAllowReturnTransitionOverlap">true</item>
    <item name="android:windowSharedElementEnterTransition">@android:transition/move</item>
    <item name="android:windowSharedElementExitTransition">@android:transition/move</item>
    <item name="android:typeface">serif</item>
</style>

Answer 2

迭代哈维特的回答：

let f (x:int) (y:int) (p:Path) : int Option =
    p |> Seq.tryPick (function
                      | x', y', z' when x = x' && y = y' -> Some z'
                      | _ -> None)

tryPick基本上只需一步即可查找和映射。

Answer 3

这是一个非常整洁的解决方案fold

let f x y p = Set.fold (function |None -> (fun  (x_,y_,z) -> if x=x_ && y=y_ then Some z else None) |f ->fun _ -> f) None p

Answer 4

这是你想要做的吗？

let f (x:int) (y:int) (p:Path) : int Option =
    match p |> Set.filter (fun (x', y', _) -> x' = x && y' = y) |> Set.toList with
    | [(_, _, z)] -> Some z
    | [] -> None
    | _ -> failwith "More than one point was found!"

示例：

> let p:Path = Set.ofList [ (0, 1, 100); (1, 1, 500); (1, 2, 50); ];;

val p : Path = set [(0, 1, 100); (1, 1, 500); (1, 2, 50)]

> f 1 2 p;;
val it : Option<int> = Some 50

从F＃中获取元组集中的元素

4 个答案: