Is there a function that checks if a character in a string is a letter in the alphabet? (Swift)

Question

I'm converting a python programme into swift, and one section uses a for loop to keep every character within a string if it is a letter. In python, it's as simple as using '.isalpha()', is there anything in swift that does this? Code in python:

word = 'hello 123'
new_word = []
for i in word:
    if i.isalpha():
        new_word.append(i)

Possible duplicate of http://stackoverflow.com/questions/24502669/swift-how-to-find-out-if-letter-is-alphanumeric-or-digit. — Martin R, May 29 '15 at 21:39

Leo Dabus · Accepted Answer · 2016-08-08T00:23:48.010

2

Xcode 8 beta4 • Swift 3

extension String {
    var lettersOnly: String {
        return components(separatedBy: CharacterSet.letters.inverted).joined(separator:"")
    }
    var lettersArray: [Character] {
        return Array(lettersOnly.characters)
    }
}

Xcode 7.3.1 • Swift 2.2.1

extension String {
    var lettersOnly: String {
        return componentsSeparatedByCharactersInSet(NSCharacterSet.letterCharacterSet().invertedSet).joinWithSeparator("")
    }
    var lettersArray: [Character] {
        return Array(lettersOnly.characters)
    }
}

Swift 1.x

import UIKit

extension String {

    var lettersOnly: String {
        return "".join(componentsSeparatedByCharactersInSet(NSCharacterSet.letterCharacterSet().invertedSet))
    }
    var lettersArray: [Character] {
        return Array("".join(componentsSeparatedByCharactersInSet(NSCharacterSet.letterCharacterSet().invertedSet)))
    }


}
let word = "hello 123"

let letters = word.lettersOnly        // "hello"

let lettersArray = word.lettersArray  // ["h", "e", "l", "l", "o"]

edited Aug 08 '16 at 00:23

answered May 29 '15 at 21:42

Leo Dabus

229,809
59
489
571

Hi, i tried this out, and i got this error: "use of unresolved identifier 'NSCharacterSet' ". Not exactly the desired result. – R21 May 29 '15 at 21:45
you need to add import UIKit or import Foundation – Leo Dabus May 29 '15 at 21:47
https://developer.apple.com/library/prerelease/ios/documentation/Cocoa/Reference/Foundation/Classes/NSCharacterSet_Class/index.html#//apple_ref/occ/clm/NSCharacterSet/letterCharacterSet – Leo Dabus May 29 '15 at 21:49
I'll try it out again later – R21 May 29 '15 at 21:50
Do you want an array of characters as result ? – Leo Dabus May 29 '15 at 22:07

score 2 · Answer 2 · answered May 29 '15 at 23:44

Why not just:

let alphabet: [Character] = [
  "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m",
  "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"
]

let word = "h4e7l2l8o1"

var answer = [String]()

for letter in word {
  if contains(alphabet, letter) {
    answer.append(String(letter))
  }
}

"".join(answer) // "hello"

or even:

let answer = "".join(filter(word) {contains(alphabet, $0)}.map{String($0)}) // "hello"

score 1 · Answer 3 · answered May 29 '15 at 22:03

1

This should work:

import Foundation // For playground or REPL

let word = "This is a string !#€%!€#% 123456 åäö é 中國"
let letterCharSet = NSCharacterSet.letterCharacterSet().invertedSet
let newWord = "".join(word.componentsSeparatedByCharactersInSet(letterCharSet))
// Outputs: "Thisisastringåäöé中國"

answered May 29 '15 at 22:03

Mikael Hellman

2,664
14
22

so does this work with any letter from any language? – R21 May 29 '15 at 22:07
Yes, might be a feature or a problem. Depending of what your looking for. :) – Mikael Hellman May 29 '15 at 22:14
This is exactly the same thing I answered. All you did was to dismantle it. – Leo Dabus May 29 '15 at 22:23
@Leonardo: Sorry did not see your answer. Had the answer window open for some time... And yes, my answer is the same as yours, and you where first and should be accepted, if the suggested approach works. – Mikael Hellman May 29 '15 at 22:26

Is there a function that checks if a character in a string is a letter in the alphabet? (Swift)

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