How to split a string at the last occurence of a sequence

Question

Target: A string with a built-in separator shall be split in an int and another string. In the case that the separator sequence '###' occurs more than once, the string shall always be spliced at the last '###'.

Is there an operator like string.lastIndexOf("###"), like in C#?

This is how my parser looks like:

func parseTuple(from string: String) -> (String, Int)? {
    let parsedString = string.components(separatedBy: "###")
    if let tupleString = String(parsedString[0]), let tupleInt = Int(parsedString[1]) {
        return (tupleString, tupleInt)
    } else {
        return nil
    }
}

Connect###Four###Player###7 should be parsed to a string "Connect###Four###Player" and to an int 7. So no matter how many '###' there are, the function shall always split the last one and leave out the remaining. — procra, Jul 03 '17 at 11:09

Martin R · Accepted Answer · 2018-05-23T13:52:41.583

The range(of:...) method of String has a .backwards option to find the last occurrence of a string. Then substring(to:) and substring(from:) can be used with the lower/upper bound of that range to extract the parts of the string preceding/following the separator:

func parseTuple(from string: String) -> (String, Int)? {

    if let theRange = string.range(of: "###", options: .backwards),
        let i = Int(string.substring(from: theRange.upperBound)) {
        return (string.substring(to: theRange.lowerBound), i)
    } else {
        return nil
    }
}

Example:

if let tuple = parseTuple(from: "Connect###Four###Player###7") {
    print(tuple)
    // ("Connect###Four###Player", 7)
}

Swift 4 update:

func parseTuple(from string: String) -> (String, Int)? {

    if let theRange = string.range(of: "###", options: .backwards),
        let i = Int(string[theRange.upperBound...]) {
        return (String(string[...theRange.lowerBound]), i)
    } else {
        return nil
    }
}

score 3 · Answer 2 · answered Jul 03 '17 at 11:20

let input = "Connect###Four###Player###7"

let seperator = "###"
// split components
var components = input.components(separatedBy: seperator)
// remove the last component ...
components = Array(components.dropLast())
// ... and re-join the remaining ones
let output = components.joined(separator: seperator)

print(output)

prints:

Connect###Four###Player

How to split a string at the last occurence of a sequence

2 Answers2

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