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Check if a key exists in a map
Given a map pets
{joe:cat,mary:turtle,bill:canary} print "ok" if an pet exists for "mary"
fsharp
if (Map.mem "mary" pets) then printfn "ok"
if pets.ContainsKey("mary") then printfn "ok"
Retrieve a value from a map
Given a map pets
{joe:cat,mary:turtle,bill:canary} print the pet for "joe" ("cat")
fsharp
if (Map.mem "joe" pets) then printfn "%s" (Map.find "joe" pets)
if (pets |> Map.exists (fun key _ -> key = "joe")) then printfn "%s" (Map.find "joe" pets)
let key = "joe"
match (pets |> Map.tryfind key) with
| Some(value) -> printfn "%s" value
| None -> printfn "Key %s not found" key
match (pets |> Map.tryfind key) with
| Some(value) -> printfn "%s" value
| None -> printfn "Key %s not found" key
if pets.ContainsKey("joe") then printfn "%s" pets.["joe"]
if pets.ContainsKey("joe") then printfn "%s" (pets.["joe"] :?> string)
Add an entry to a map
Given an empty pets map, add the mapping from
"rob" to "dog"
fsharp
pets <- (Map.add "rob" "dog" pets)
pets.Add("rob", "dog")
Remove an entry from a map
Given a map pets
{joe:cat,mary:turtle,bill:canary} remove the mapping for "bill" and print "canary"
fsharp
let key = "bill"
match (pets |> Map.tryFind key) with
| Some(value) -> pets <- (Map.remove key pets) ; printfn "%s : %s removed" key value
| None -> printfn "Key %s not found" key
match (pets |> Map.tryFind key) with
| Some(value) -> pets <- (Map.remove key pets) ; printfn "%s : %s removed" key value
| None -> printfn "Key %s not found" key
let key = "bill"
let entry = if (pets.ContainsKey(key)) then Some(pets.[key]) ; else None
pets.Remove(key)
match entry with
| Some(value) -> printfn "%s" value
| None -> printfn "key not found"
let entry = if (pets.ContainsKey(key)) then Some(pets.[key]) ; else None
pets.Remove(key)
match entry with
| Some(value) -> printfn "%s" value
| None -> printfn "key not found"
