Sequences in FSharp

Introduction: A sequence represents an ordered series of elements of the same type. Sequences are important when we work with large amounts of data. It is also known as a sequence expression. It is very similar to Lists - except only one element of sequence can be exist in memory at a time. Sequences are represented by seq<T>type, which is an alias name for System.Collections.Generic.IEnumerable<T>.

Advantages of Sequences:

We can define an infinite sequence in easily ways.
It support many functions of List.
It has several function for extracting subsequences.
It provide an easy way to define sequence of items.

Syntax for Defining a Sequence

Syntax for defining a sequence is given below.

seq { exp }

Like, seq { 1..10}

Now we create some sequences using different sequence expressions.

Write the following code:

// Sequence using Range Expressions
let one= seq { 0 .. 100 }
printfn "%A" one

//Sequence using Range Expressions of characters
let two= seq {'a'..'z'}
printfn "%A" two

//Sequence with increment
let three= seq {1..2..10}
printfn "%A" three

//sequence with yield keyword
let four= seq { for i in 1 .. 5 do yield i * i }
printfn "%A" four

//sequence with -> operator
let five= seq { for i in 1 .. 5 -> i * i }
printfn "%A" five

//Sequence with decrement
let six= seq {10..-1..1}
printfn "%A" six

Now we run this code by pressing Ctrl+F5 key.

Output

sequences in f#

Seq Module Functions

Seq.take: The Set.Take function returns the specified number of elements from a sequence. Write the following code:

let one= seq {1 .. 10 }
let takenSeq = Seq.take 2 one
printfn "%A" takenSeq

Output:

seq.take in f#

Seq.unfold: Generates a sequence using a given function. The function provide an input value and returns an option tuple of the next value of the sequence and next iteration of Seq.unfold. Write the following code:

let one = Seq.unfold (fun state -> if (state > 10) then None else Some(state, state + 1)) 0
for n in one do
printfn "%d " n

Output:

Seq.toList: The Seq.toList function creates a list from the given collection. Write the following code:

let one = seq { 1..10 }
let two = Seq.toList one
printfn "%A" two

Output:

seq.tolist in f#

Aggregate Operators in Sequence: Seq module aggregate operators. Some of these are given below.

Seq.iter: It iterates the given function for each element of a sequence, Like the below example.

let one = seq { 1 .. 10 }
Seq.iter (printfn "%d") one

Output:

Seq.map: It creates a new sequence whose element is the outcome of applying the given function over the old sequence. Write the following code:

let one = [|1; 2; 3;4;5|]
let two = one |> Seq.map (fun x -> x * x)
printfn "%A" one
printfn "%A" two

Output: