在F#中,地图是一种特殊的集合,它将值与键相关联.创建地图的方式与创建集合的方式类似.
通过使用Map.empty创建空地图来创建地图使用"添加"功能添加项目.以下示例演示了此 :
(* 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
当你编译并执行程序时,它会产生以下输出 :
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")]
您可以使用密钥访问地图中的各个元素.
(* 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,它会产生以下输出 :
Map - students: map [("Gillian Megan", "1504"); ("Rishita Gupta", "1502"); ("Robin Sahoo", "1503 "); ("Zara Ali", "1501")] "1501"
下表显示了map&minus的基本操作;
会员 | 描述 |
---|---|
Add | 返回添加到给定地图的绑定的新地图. |
ContainsKey | 测试元素是否在地图的域中. |
计数 | 地图中绑定的数量. |
IsEmpty | 如果地图中没有绑定,则返回true. |
Item | 在地图中查找元素.如果地图中不存在绑定,则引发KeyNotFoundException. |
Remove | 删除来自地图领域的元素.如果元素不存在,则不会引发异常. |
TryFind | 查找地图中的元素,如果元素位于地图的域中,则返回 Some 值;如果不是,则返回无. |
以下示例演示了上述某些功能的使用 :
(* 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,它会产生以下输出 :
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.