Count the number of lines in a Swift String

Question

After reading a medium sized file (about 500kByte) from a web-service I have a regular Swift String (lines) originally encoded in .isolatin1. Befor

Answer 1

As I did not find a generic way to count newlines I ended up just solving my problem by iterating through all the characters using

let linesCount = text.reduce(into: 0) { (count, letter) in
     if letter == "\r\n" {      // This treats CRLF as one "letter", contrary to UnicodeScalars
        count += 1
     }
}

I was sure this would be a lot faster than enumerating lines for just counting, but I resolved to eventually do the measurement. Today I finally got to it and found ... that I could not have been more wrong.

A 10000 line string counted lines as above in about 1.0 seconds , but counting through enumeration using

var enumCount = 0
text.enumerateLines { (str, _) in
    enumCount += 1
}

only took around 0.8 seconds and was consistently faster by a little more than 20%. I do not know what tricks the Swift engineers hide in their sleves, but they sure manage to enumerateLines very quickly. This just for the record.

Answer 2

If it's ok for you to use a Foundation method on an NSString, I suggest using

enumerateLines(_ block: @escaping (String, UnsafeMutablePointer<ObjCBool>) -> Void)

Here's an example:

import Foundation

let base = "Hello, playground\r\nhere too\r\nGalahad\r\n"
let ns = base as NSString

ns.enumerateLines { (str, _) in
    print(str)
}

It separates the lines properly, taking into account all linefeed types, such as "\r\n", "\n", etc:

Hello, playground
here too
Galahad

In my example I print the lines but it's trivial to count them instead, as you need to - my version is just for the demonstration.

Answer 3

Swift 5 Extension

extension String {
    
    func numberOfLines() -> Int {
        return self.numberOfOccurrencesOf(string: "\n") + 1
    }
    
}

Example:

let testString = "First line\nSecond line\nThird line"
let numberOfLines = testString.numberOfLines() // returns 3