How add separator to string at every N characters in swift?
Swift 5.2 • Xcode 11.4 or later
extension Collection {
func unfoldSubSequences(limitedTo maxLength: Int) -> UnfoldSequence<SubSequence,Index> {
sequence(state: startIndex) { start in
guard start < endIndex else { return nil }
let end = index(start, offsetBy: maxLength, limitedBy: endIndex) ?? endIndex
defer { start = end }
return self[start..<end]
}
}
func every(n: Int) -> UnfoldSequence<Element,Index> {
sequence(state: startIndex) { index in
guard index < endIndex else { return nil }
defer { let _ = formIndex(&index, offsetBy: n, limitedBy: endIndex) }
return self[index]
}
}
var pairs: [SubSequence] { .init(unfoldSubSequences(limitedTo: 2)) }
}
extension StringProtocol where Self: RangeReplaceableCollection {
mutating func insert<S: StringProtocol>(separator: S, every n: Int) {
for index in indices.every(n: n).dropFirst().reversed() {
insert(contentsOf: separator, at: index)
}
}
func inserting<S: StringProtocol>(separator: S, every n: Int) -> Self {
.init(unfoldSubSequences(limitedTo: n).joined(separator: separator))
}
}
Testing
let str = "112312451"
let final0 = str.unfoldSubSequences(limitedTo: 2).joined(separator: ":")
print(final0) // "11:23:12:45:1"
let final1 = str.pairs.joined(separator: ":")
print(final1) // "11:23:12:45:1"
let final2 = str.inserting(separator: ":", every: 2)
print(final2) // "11:23:12:45:1\n"
var str2 = "112312451"
str2.insert(separator: ":", every: 2)
print(str2) // "11:23:12:45:1\n"
var str3 = "112312451"
str3.insert(separator: ":", every: 3)
print(str3) // "112:312:451\n"
var str4 = "112312451"
str4.insert(separator: ":", every: 4)
print(str4) // "1123:1245:1\n"
I'll go for this compact solution (in Swift 4) :
let s = "11231245"
let r = String(s.enumerated().map { $0 > 0 && $0 % 2 == 0 ? [":", $1] : [$1]}.joined())
You can make an extension and parameterize the stride and the separator so that you can use it for every value you want (In my case, I use it to dump 32-bit space-operated hexadecimal data):
extension String {
func separate(every stride: Int = 4, with separator: Character = " ") -> String {
return String(enumerated().map { $0 > 0 && $0 % stride == 0 ? [separator, $1] : [$1]}.joined())
}
}
In your case this gives the following results:
let x = "11231245"
print (x.separate(every:2, with: ":")
$ 11:23:12:45