How to split a string by new lines in Swift

Question

I have a string that I got from a text file.

Text file:

Line 1
Line 2
Line 3
...

I want to convert it to an array, one array element p

Answer 1

In Swift 2, the top-level split function is now a method on CollectionType (which each of Strings "character views" conforms to). There are two versions of the method, you want the one that takes a closure as a predicate to indicate whether a given element should be treated as a separator.

You can get the character collection from the string as a collection of UTF16 characters using string.utf16, making them compatible with the NSCharacterSet APIs. This way, we can easily check inside the closure whether a given character in the string is a member of the newline character set.

It's worth noting that split(_:) will return a SubSequence of characters (basically a Slice), so it needs transforming back into an array of Strings which is generally more useful. I've done this below using flatMap(String.init) - the UTF16View initialiser on String is failable, so using flatMap will ignore any nil values that might be returned, ensuring you get an array of non-optional strings back.

So for a nice Swift-like way of doing this:

let str = "Line 1\nLine 2\r\nLine 3\n"
let newlineChars = NSCharacterSet.newlineCharacterSet()
let lines = str.utf16.split { newlineChars.characterIsMember($0) }.flatMap(String.init)
// lines = ["Line 1", "Line 2", "Line 3"]

What makes this nice is that the split method has a parameter allowEmptySubsequences, which ensures you don't receive any empty character sequences in the result. This is false by default, so you don't actually need to specify it at all.

Edit

If you want to avoid NSCharacterSet altogether, you can just as easily split the collection of unicode compliant Characters.

let lines = str.characters.split { $0 == "\n" || $0 == "\r\n" }.map(String.init)

Swift is able to treat "\r\n" as a single extended grapheme cluster, using it as a single Character for the comparison instead of creating a String. Also note that the initialiser for creating a string from a Character is non failable, so we can just use map.