How to Filter Characters from a String in Swift 4

How to filter characters from a string in Swift 4

Swift 4 makes it a little simpler. Just remove the .characters and use

let myNumbers = myString.filter { "0123456789".contains($0) }

But to really do it properly, you might use the decimalDigits character set...

let digitSet = CharacterSet.decimalDigits
let myNumbers = String(myString.unicodeScalars.filter { digitSet.contains($0) })

Swift - Remove character from string

Swift uses backslash to escape double quotes. Here is the list of escaped special characters in Swift:

• \0 (null character)
• \\ (backslash)
• \t (horizontal tab)
• \n (line feed)
• \r (carriage return)
• \" (double quote)
• \' (single quote)

This should work:

text2 = text2.replacingOccurrences(of: "\\", with: "", options: NSString.CompareOptions.literal, range: nil)

Looking for the best way to filter text from string in Swift

One way to do this is to first map the strings to a tuple containing the index of the search text in string, and the string itself. Then sort by the index, then map the tuples back to the strings.

let array = ["Anand", "Ani", "Dan", "Eion", "Harsh", "Jocab", "Roshan", "Stewart"]
let searchText = "R"
// compactMap acts as a filter, removing the strings where string.index(of: searchText, options: [.caseInsensitive]) returns nil
let result = array.compactMap { string in string.index(of: searchText, options: [.caseInsensitive]).map { ($0, string) } }
                    .sorted { $0.0 < $1.0 }.map { $0.1 }

The index(of:options:) method is taken from this answer here.

For Swift 4.x:

extension StringProtocol where Index == String.Index {
    func index(of string: Self, options: String.CompareOptions = []) -> Index? {
        return range(of: string, options: options)?.lowerBound
    }
    func endIndex(of string: Self, options: String.CompareOptions = []) -> Index? {
        return range(of: string, options: options)?.upperBound
    }
    func indexes(of string: Self, options: String.CompareOptions = []) -> [Index] {
        var result: [Index] = []
        var startIndex = self.startIndex
        while startIndex < endIndex,
            let range = self[startIndex...].range(of: string, options: options) {
                result.append(range.lowerBound)
                startIndex = range.lowerBound < range.upperBound ? range.upperBound :
                    index(range.lowerBound, offsetBy: 1, limitedBy: endIndex) ?? endIndex
        }
        return result
    }
    func ranges(of string: Self, options: String.CompareOptions = []) -> [Range<Index>] {
        var result: [Range<Index>] = []
        var startIndex = self.startIndex
        while startIndex < endIndex,
            let range = self[startIndex...].range(of: string, options: options) {
                result.append(range)
                startIndex = range.lowerBound < range.upperBound ? range.upperBound :
                    index(range.lowerBound, offsetBy: 1, limitedBy: endIndex) ?? endIndex
        }
        return result
    }
}

How do I filter an array of Strings to a unique result in Swift

A solution is to use Regular Expression to search for word boundaries

func filterWaypoint(searchString: String, array: [String]) -> String {
    let result = array.filter { $0.range(of: "\\b\(searchString)\\b", options: [.regularExpression, .caseInsensitive]) != nil }
    print(result)
    return result.first ?? ""
}

Remove all non-numeric characters from a string in swift

I was hoping there would be something like stringFromCharactersInSet() which would allow me to specify only valid characters to keep.

You can either use trimmingCharacters with the inverted character set to remove characters from the start or the end of the string. In Swift 3 and later:

let result = string.trimmingCharacters(in: CharacterSet(charactersIn: "0123456789.").inverted)

Or, if you want to remove non-numeric characters anywhere in the string (not just the start or end), you can filter the characters, e.g. in Swift 4.2.1:

let result = string.filter("0123456789.".contains)

Or, if you want to remove characters from a CharacterSet from anywhere in the string, use:

let result = String(string.unicodeScalars.filter(CharacterSet.whitespaces.inverted.contains))

Or, if you want to only match valid strings of a certain format (e.g. ####.##), you could use regular expression. For example:

if let range = string.range(of: #"\d+(\.\d*)?"#, options: .regularExpression) {
    let result = string[range] // or `String(string[range])` if you need `String`
}

The behavior of these different approaches differ slightly so it just depends on precisely what you're trying to do. Include or exclude the decimal point if you want decimal numbers, or just integers. There are lots of ways to accomplish this.

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For older, Swift 2 syntax, see previous revision of this answer.

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