Swift equivalent for Java indexOf and lastIndexOf of a string

Question

I come from Java. I studied the Swift documentation and understood most of the concepts.

What I now looking for is an equivalent to the Java indexOf and lastIndexOf methods to finding positions of substring in a string.

I already found a solution with rangeOfString and using the startIndex property. That looks helpful for me to define the indexOf method.

But I think that rangeOfString only starts searching from the beginning of a string. Is this correct? And if so, how can I search in reverse direction (from end to start of the string)?

What I mean is to have f.e. the string "hello world" and if I start searching for "l" then I want to find the letter at position 9 and not at position 2.

Have a look at stackoverflow.com/questions/28182441/…, it shows various methods, including the .BackwardsSearch option. — Martin R
– Martin R, Commented Sep 30, 2016 at 11:41
You can use "some string".characters.indexOf('someChar') but it only works for chars.. — Dan
– Dan, Commented Sep 30, 2016 at 12:06

Danyl Semmache · Accepted Answer · 2017-04-05 20:04:04Z

27

+50

In Swift 3

Java indexOf equivalent:

var index1 = string1.index(string1.endIndex, offsetBy: -4)

Java lastIndexOf equivalent:

 var index2 = string2.range(of: ".", options: .backwards)?.lowerBound

answered Apr 5, 2017 at 20:04

Danyl Semmache

2,0623 gold badges22 silver badges40 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

John Difool Over a year ago

Why do you have offsetBy: -4 for the indexOf ?

Patrick Over a year ago

@Laurent indexOf has an optional fromIndex: beginnersbook.com/2013/12/java-string-indexof-method-example

Neph Over a year ago

In Swift 5 the "lastIndexOf" code returns a String.Index, not an Int (like in Java). You could as well just do mystring.lastIndex(of: "."), which is shorter and also returns a String.Index. The problem is that there doesn't seem to be an easy way to convert that into a proper Int you can work with.

Vladimir Kofman · Accepted Answer · 2017-04-14 19:23:18Z

8

extension String {
    func indexOf(_ input: String,
                 options: String.CompareOptions = .literal) -> String.Index? {
        return self.range(of: input, options: options)?.lowerBound
    }

    func lastIndexOf(_ input: String) -> String.Index? {
        return indexOf(input, options: .backwards)
    }
}

"hello world".indexOf("l") // 2
"hello world".lastIndexOf("l") // 9

answered Apr 14, 2017 at 19:23

Vladimir Kofman

1,99321 silver badges21 bronze badges

2 Comments

Neph Over a year ago

Printing the tests results in: 1. Optional(Swift.String.Index(_rawBits: 131072)), 2. Optional(Swift.String.Index(_rawBits: 589824)) - how did you get the actual int from it?

chitgoks Over a year ago

Problem is using this in substring.

Aviv Ben Shabat · Accepted Answer · 2018-01-30 15:48:21Z

8

If you want the returned value to be an Int:

extension String {

    func lastIndex(of string: String) -> Int? {
        guard let index = range(of: string, options: .backwards) else { return nil }
        return self.distance(from: self.startIndex, to: index.lowerBound)
    }
}

answered Jan 30, 2018 at 15:48

Aviv Ben Shabat

1,1032 gold badges13 silver badges33 bronze badges

Comments

paddy · Accepted Answer · 2018-12-16 01:01:46Z

0

There is a built in swift function for finding the index of last occurrence of a character. The function signature is below

public func lastIndex(of element: Character) -> String.Index?{}

We can get the index for a character like below:

let url = "http://www.google.com/abc"
guard let lastIndexOfChar = url.lastIndex(of: "/") else { return nil }
let startIndex = url.index(lastIndexOfChar, offsetBy:1)
let substring = url[startIndex..<url.endIndex] // prints "abc"

answered Dec 16, 2018 at 1:01

paddy

471 silver badge7 bronze badges

Collectives™ on Stack Overflow

Swift equivalent for Java indexOf and lastIndexOf of a string

4 Answers 4

3 Comments

2 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related