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In F#, a map is a special kind of set that associates the values with key. A map is created in a similar way as sets are created.
Creating Maps
Maps are created by creating an empty map using Map.empty and adding items using the Add function. The following example demonstrates this −
Example
(* 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
When you compile and execute the program, it yields the following output −
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")]
You can access individual elements in the map using the key.
Example
(* 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"]
When you compile and execute the program, it yields the following output −
Map - students: map
[("Gillian Megan", "1504"); ("Rishita Gupta", "1502"); ("Robin Sahoo", "1503
");
("Zara Ali", "1501")]
"1501"
Basic Operations on Maps
Add module name
The following table shows the basic operations on maps −
| 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. |
The following example demonstrates the uses of some of the above functionalities −
Example
(* 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."
When you compile and execute the program, it yields the following output −
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.
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