FSharp for Beginners: What is the List.Map Function?

The List.map function creates a new collection by applying a function to the given collection.

 

Just have a look at the below example,



When you print r1 you should get output like 2,3,4,5

let data = [1;2;3;4]
let functiontomap  r = r+ 1 
let r1 =  List.map functiontomap data  
printfn "updated data  = %A" r1
open System 
printfn "Press any key to continue"
Console.ReadKey(true);

Expected output



In previous example, I explicitly defined the input function, however, it is not required, you can use List.map as below:



In the above way of using List.map, we are directly applying a function to the input collection.

let data = [1..10]
let resultincrement = data |> List.map (fun x -> x + 1)
let resultsquare = data |> List.map (fun x -> x*x)
printfn "incremented data  = %A" resultincrement
printfn "squared data = %A" resultsquare
open System 
printfn "Press any key to continue"
Console.ReadKey(true);

Expected output



If you want to covert the above integer collection to strings, that also is very much possible in a single line statement, like below:



As the input function you need to pass a string

let data = [1..10]
let stringdata = data |> List.map string 
printfn "String data = %A" stringdata
open System 
printfn "Press any key to continue"
Console.ReadKey(true);

Expected output



I hope this post was useful. Thanks for reading

If you find my posts useful you may like to follow me on twitter http://twitter.com/debug_mode or may like Facebook page of my blog http://www.facebook.com/DebugMode.Net If you want to see post on a particular topic please do write on FB page or tweet me about that, I would love to help you.