F# - Sets

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A set in F# is a data structure that acts as a collection of items without preserving the order in which items are inserted. Sets do not allow duplicate entries to be inserted into the collection.

Creating Sets

Sets can be created in the following ways −

• By creating an empty set using Set.empty and adding items using the add function.
• Converting sequences and lists to sets.

The following program demonstrates the techniques −

(* creating sets *)
let set1 = Set.empty.Add(3).Add(5).Add(7). Add(9)
printfn"The new set: %A" set1

let weekdays = Set.ofList ["mon"; "tues"; "wed"; "thurs"; "fri"]
printfn "The list set: %A" weekdays

let set2 = Set.ofSeq [ 1 .. 2.. 10 ]
printfn "The sequence set: %A" set2

When you compile and execute the program, it yields the following output −

The new set: set [3; 5; 7; 9]
The list set: set ["fri"; "mon"; "thurs"; "tues"; "wed"]
The sequence set: set [1; 3; 5; 7; 9]

Basic Operations on Sets

The following table shows the basic operations on sets −

The following example demonstrates the uses of some of the above functionalities −

Example

let a = Set.ofSeq [ 1 ..2.. 20 ]
let b = Set.ofSeq [ 1 ..3 .. 20 ]
let c = Set.intersect a b
let d = Set.union a b
let e = Set.difference a b

printfn "Set a: "
Set.iter (fun x -> printf "%O " x) a
printfn""

printfn "Set b: "
Set.iter (fun x -> printf "%O " x) b
printfn""

printfn "Set c = set intersect of a and b : "
Set.iter (fun x -> printf "%O " x) c
printfn""

printfn "Set d = set union of a and b : "
Set.iter (fun x -> printf "%O " x) d
printfn""

printfn "Set e = set difference of a and b : "
Set.iter (fun x -> printf "%O " x) e
printfn""

When you compile and execute the program, it yields the following output −

Set a:
1 3 5 7 9 11 13 15 17 19
Set b:
1 4 7 10 13 16 19
Set c = set intersect of a and b :
1 7 13 19
Set d = set union of a and b :
1 3 4 5 7 9 10 11 13 15 16 17 19
Set e = set difference of a and b :
3 5 9 11 15 17