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📜  F＃-地图

📅  最后修改于: 2020-11-21 06:50:34             🧑  作者: Mango

在F＃中，映射是一种特殊的集合，它将值与键相关联。映射的创建方式与集合的创建方式类似。

创建地图

通过使用Map.empty创建一个空地图并使用Add函数添加项目来创建地图。以下示例演示了这一点-

例

现场演示
(* Create an empty Map *)
let students =
   Map.empty. (* Creating an empty Map *)
      Add("Zara Ali", "1501").
      Add("Rishita Gupta", "1502").
      Add("Robin Sahoo", "1503").
      Add("Gillian Megan", "1504");;
printfn "Map - students: %A" students

(* Convert a list to Map *)
let capitals =
   [ "Argentina", "Buenos Aires";
      "France ", "Paris";
      "Chili", "Santiago";
      "Malaysia", " Kuala Lumpur";
      "Switzerland", "Bern" ]
   |> Map.ofList;;
printfn "Map capitals : %A" capitals

编译并执行程序时，将产生以下输出-

Map - students: map
[("Gillian Megan", "1504"); ("Rishita Gupta", "1502"); ("Robin Sahoo", "1503
");
("Zara Ali", "1501")]
Map capitals : map
[("Argentina", "Buenos Aires"); ("Chili", "Santiago"); ("France ", "Paris");
("Malaysia", " Kuala Lumpur"); ("Switzerland", "Bern")]

您可以使用键访问地图中的各个元素。

例

现场演示
(* Create an empty Map *)
let students =
   Map.empty. (* Creating an empty Map *)
      Add("Zara Ali", "1501").
      Add("Rishita Gupta", "1502").
      Add("Robin Sahoo", "1503").
      Add("Gillian Megan", "1504");;
printfn "Map - students: %A" students

(*Accessing an element using key *)
printfn "%A" students.["Zara Ali"]

编译并执行程序时，将产生以下输出-

Map - students: map
[("Gillian Megan", "1504"); ("Rishita Gupta", "1502"); ("Robin Sahoo", "1503
");
("Zara Ali", "1501")]
"1501"

地图的基本操作

添加模块名称

下表显示了地图上的基本操作-

Member Description
Add Returns a new map with the binding added to the given map.
ContainsKey Tests if an element is in the domain of the map.
Count The number of bindings in the map.
IsEmpty Returns true if there are no bindings in the map.
Item Lookup an element in the map. Raises KeyNotFoundException if no binding exists in the map.
Remove Removes an element from the domain of the map. No exception is raised if the element is not present.
TryFind Lookup an element in the map, returning a Some value if the element is in the domain of the map and None if not.

以下示例演示了上述某些功能的用法-

例

现场演示
(* Create an empty Map *)
let students =
   Map.empty. (* Creating an empty Map *)
      Add("Zara Ali", "1501").
      Add("Rishita Gupta", "1502").
      Add("Robin Sahoo", "1503").
      Add("Gillian Megan", "1504").
      Add("Shraddha Dubey", "1505").
      Add("Novonil Sarker", "1506").
      Add("Joan Paul", "1507");;
printfn "Map - students: %A" students
printfn "Map - number of students: %d" students.Count

(* finding the registration number of a student*)
let found = students.TryFind "Rishita Gupta"
match found with
| Some x -> printfn "Found %s." x
| None -> printfn "Did not find the specified value."

编译并执行程序时，将产生以下输出-

Map - students: map
[("Gillian Megan", "1504"); ("Joan Paul", "1507"); ("Novonil Sarker", "1506"
);
("Rishita Gupta", "1502"); ("Robin Sahoo", "1503");
("Shraddha Dubey", "1505"); ("Zara Ali", "1501")]
Map - number of students: 7
Found 1502.