How to find multiple substrings within braces from a string? - ios

Question

I have a string [Desired Annual Income] /([Income per loan %] /100)
Using this string, I have to find two sub strings 'Desired Annual Income' and 'Income per loan %' in Swift3.
I am using below code to achieve this 'How do I get the substring between braces?':
let myString = "[Desired Annual Income] /([Income per loan %] /100)"
let start: NSRange = (myString as NSString).range(of: "[")
let end: NSRange = (myString as NSString).range(of: "]")
if start.location != NSNotFound && end.location != NSNotFound && end.location > start.location {
let result: String = (myString as NSString).substring(with: NSRange(location: start.location + 1, length: end.location - (start.location + 1)))
print(result)
}
But as an output I am getting only 'Desired Annual Income', How can I get all substrings?

Answer 1

Try this,
Hope it will work
let str = "[Desired Annual Income] /([Income per loan %] /100)"
let trimmedString = str.components(separatedBy: "]")
for i in 0..<trimmedString.count - 1{ // not considering last component since it's of no use hence count-1 times loop
print(trimmedString[i].components(separatedBy: "[").last ?? "")
}
Output:-
Desired Annual Income
Income per loan %

Answer 2

It's a very good use case for regular expressions (NSRegularExpression). The principle of regular expressions is to describe a "pattern" that you want to search in a string.
In that case you search something between two brackets.
The code is then:
let str = "[Desired Annual Income] /([Income per loan %] /100)"
if let regex = try? NSRegularExpression(pattern: "\\[(.+?)\\]", options: [.caseInsensitive]) {
var collectMatches: [String] = []
for match in regex.matches(in: str, options: [], range: NSRange(location: 0, length: (str as NSString).length)) {
// range at index 0: full match (including brackets)
// range at index 1: first capture group
let substring = (str as NSString).substring(with: match.range(at: 1))
collectMatches.append(substring)
}
print(collectMatches)
}
For the explanation about regular expressions, there are plenty of tutorial on internet. But in very short:
\\[ and \\]: opening and closing brackets characters (the double backslashes are because brackets have a meaning in regular expression, so you need to escape them. In a text editor one backslash is enough, but you need a second one because you are in a String and you need to escape the backslash to have a backslash.
(.+?) is a bit more complex: the parentheses are the "capture group", what you want to get. . means "any character", + one or more time, ? after a + is the greedy operator, which means that you want the capture to stop ASAP. If you don't put it, your capture can be in your case "Desired Annual Income] /([Income per loan %", depending of the regex library that you are using. Foundation seems to be greedy by default, that being said.
Regex are not always super easy/direct, but if you do often text processing, it's a very powerful tool to know.