Split

A string contains many values. It has names of animals separated by commas. We must split this string. Splitting is not exciting, but it is useful.

With Split, a method on the String type in .NET, we receive a String array. And with the helpful Seq.toList we can convert this into an F# list for further use.

Simple example

We introduce a string with three fields separated by commas. We call the Split method with a single comma char—this is expanded to a char array.

let animals = "bear,frog,eagle"

// Split on the comma.
// ... This is creating a single-element character array for us.
let result = animals.Split ','

// Loop over and display strings.
for value in result do
    printfn "%A" value
"bear"
"frog"
"eagle"

Seq.toList

This example adds some complexity. We introduce a splitLine function. This receives a string and calls Split on it. Then it returns the result of Seq.toList.

// Create a splitLine function.
// ... It uses Seq.toList on the result of line.Split.
//     So we can access a list.
let splitLine = (fun (line : string) -> Seq.toList (line.Split ','))

// Split this line into a list.
let plants = "turnip,carrot,lettuce"
let result = splitLine plants

// Display our results in a for-loop.
for value in result do
    printfn "%A" value
"turnip"
"carrot"
"lettuce"

String separator

With Split() we can separate a string based on a substring delimiter. We create a string array containing all delimiters and pass it to Split.

open System
let items = "keyboard; mouse; ; monitor"

// Call split with a string array as the first argument.
// ... This splits on a two-char sequence.
//     Also remove empty array elements.
let result = items.Split([|"; "|], StringSplitOptions.RemoveEmptyEntries)

// Print all elements in the array with Seq.iter.
Seq.iter (fun x -> printfn "%A" x) result
"keyboard"
"mouse"
"monitor"

Multiple delimiters

Here we Split on 2 different character delimiters. We provide a char array to Split() as the first argument. We use a for-loop to print results.

let clothes = "pants.shoes:socks"

// Split on two different characters.
let result = clothes.Split([|'.'; ':'|])

// Print results with for-loop.
for r in result do
    printfn "%s" r
pants
shoes
socks

F# adds no special splitting methods. But it allows easy access to the powerful .NET Framework string split method. With some conversion, we can split into a list.