在F#中，字典(Maps)是一种特殊的集合，将值(value)与键(key)相关联。
创建字典
通过使用Map.empty创建空Map并使用添加功能添加项目来创建Map。以下示例演示了这一点-
(* 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Map中的各个元素。
(* 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"
基本操作
下表显示了Map上的基本操作-
| 方法 | 说明 |
|---|---|
| Add | 返回新Map,并将绑定添加到给定Map。 |
| ContainsKey | 测试元素是否在Map的域中。 |
| Count | Map中的绑定数。 |
| IsEmpty | 如果Map中没有绑定,则返回true。 |
| Item | 在Map中查找元素。如果Map中没有绑定,则引发KeyNotFoundException。 |
| Remove | 从Map的域中删除一个元素。如果元素不存在,则不会引发异常。 |
| TryFind | 在Map中查找元素,如果元素在Map的域中,则返回 Some 值,否则返回 None 。 |
以下示例演示了上述某些功能的用法-
(* 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.
参考链接
https://www.learnfk.com/fsharp/fsharp-maps.html
标签：Map,映射,students,无涯,Maps,Add,Zara,printfn,empty From： https://blog.51cto.com/u_14033984/8604945