CODEWITHSUNDEEP
stringswift
SSteve
SSteve

Reputation: 10728

What is the most succinct way to remove the first character from a string in Swift?

I want to delete the first character from a string. So far, the most succinct thing I've come up with is:

display.text = display.text!.substringFromIndex(advance(display.text!.startIndex, 1))

I know we can't index into a string with an Int because of Unicode, but this solution seems awfully verbose. Is there another way that I'm overlooking?

Upvotes: 162

Views: 132683

Answers (13)

jason z
jason z

Reputation: 1377

Depends on what what you want the end result to be (mutating vs nonmutating).

As of Swift 4.1:

Mutating:

var str = "hello"
str.removeFirst() // changes str

Nonmutating:

let str = "hello"
let strSlice = str.dropFirst() // makes a slice without the first letter
let str2 = String(strSlice)

Notes:

  • I put an extra step in the nonmutating example for clarity. Subjectively, combining the last two steps would be more succinct.
  • The naming of dropFirst seems a bit odd to me because if I am understanding the Swift API Design Guidelines correctly, dropFirst should really be something like droppingFirst because it is nonmutating. Just a thought :).

Upvotes: 18

neoneye
neoneye

Reputation: 52181

Swift3

extension String {
    func chopPrefix(_ count: UInt = 1) -> String {
        return substring(from: characters.index(startIndex, offsetBy: Int(count)))
    }

    func chopSuffix(_ count: UInt = 1) -> String {
        return substring(to: characters.index(endIndex, offsetBy: -Int(count)))
    }
}

class StringChopTests: XCTestCase {
    func testPrefix() {
        XCTAssertEqual("original".chopPrefix(0), "original")
        XCTAssertEqual("Xfile".chopPrefix(), "file")
        XCTAssertEqual("filename.jpg".chopPrefix(4), "name.jpg")
    }

    func testSuffix() {
        XCTAssertEqual("original".chopSuffix(0), "original")
        XCTAssertEqual("fileX".chopSuffix(), "file")
        XCTAssertEqual("filename.jpg".chopSuffix(4), "filename")
    }
}

Upvotes: 1

Mohamed Jaleel Nazir
Mohamed Jaleel Nazir

Reputation: 5821

Swift 2.2

'advance' is unavailable: call the 'advancedBy(n)' method on the index

    func chopPrefix(count: Int = 1) -> String {
        return self.substringFromIndex(self.startIndex.advancedBy(count))
    }

    func chopSuffix(count: Int = 1) -> String {
        return self.substringFromIndex(self.endIndex.advancedBy(count))
    }

Swift 3.0

    func chopPrefix(_ count: Int = 1) -> String {
        return self.substring(from: self.characters.index(self.startIndex, offsetBy: count))
    }

    func chopSuffix(_ count: Int = 1) -> String {
       return self.substring(to: self.characters.index(self.endIndex, offsetBy: -count))
    }

Swift 3.2

A view of the string's contents as a collection of characters.

@available(swift, deprecated: 3.2, message: "Please use String or Substring directly")
public var characters: String.CharacterView

func chopPrefix(_ count: Int = 1) -> String {
    if count >= 0 && count <= self.count {
        return self.substring(from: String.Index(encodedOffset: count))
    }
    return ""
}

func chopSuffix(_ count: Int = 1) -> String {
    if count >= 0 && count <= self.count {
        return self.substring(to: String.Index(encodedOffset: self.count - count))
    }
    return ""
}

Swift 4

extension String {

    func chopPrefix(_ count: Int = 1) -> String {
        if count >= 0 && count <= self.count {
            let indexStartOfText = self.index(self.startIndex, offsetBy: count)
            return String(self[indexStartOfText...])
        }
        return ""
    }

    func chopSuffix(_ count: Int = 1) -> String {
        if count >= 0 && count <= self.count {
            let indexEndOfText = self.index(self.endIndex, offsetBy: -count)
            return String(self[..<indexEndOfText])
        }
        return ""
    }
}

Upvotes: 18

ByteSlinger
ByteSlinger

Reputation: 1597

The previous answers are pretty good, but as of today, I think this may be the most succinct way to remove the first character from a string in Swift 4:

var line: String = "This is a string..."
var char: Character? = nil

char = line.removeFirst()

print("char = \(char)")  // char = T
print("line = \(line)")  // line = his is a string ...

Upvotes: 7

iDoc
iDoc

Reputation: 461

Here is a Swift4 crash save version of the chopPrefix extension, leaving chopSuffix to the community ...

extension String {
    func chopPrefix(_ count: Int = 1) -> String {
        return count>self.count ? self : String(self[index(self.startIndex, offsetBy: count)...])
    }
 }

Upvotes: 0

vacawama
vacawama

Reputation: 154583

Update for Swift 4

In Swift 4, String conforms to Collection again, so it is possible to use dropFirst and dropLast to trim the beginnings and ends of strings. The result is of type Substring, so you need to pass that to the String constructor to get back a String:

let str = "hello"
let result1 = String(str.dropFirst())    // "ello"
let result2 = String(str.dropLast())     // "hell"

dropFirst() and dropLast() also take an Int to specify the number of characters to drop:

let result3 = String(str.dropLast(3))    // "he"
let result4 = String(str.dropFirst(4))   // "o"

If you specify more characters to drop than are in the string, the result will be the empty string ("").

let result5 = String(str.dropFirst(10))  // ""

Update for Swift 3

If you just want to remove the first character and want to change the original string in place, then see @MickMacCallum's answer. If you want to create a new string in the process, use substring(from:). With an extension to String, you can hide the ugliness of substring(from:) and substring(to:) to create useful additions to trim the start and ends of a String:

extension String {
    func chopPrefix(_ count: Int = 1) -> String {
        return substring(from: index(startIndex, offsetBy: count))
    }

    func chopSuffix(_ count: Int = 1) -> String {
        return substring(to: index(endIndex, offsetBy: -count))
    }
}

"hello".chopPrefix()    // "ello"
"hello".chopPrefix(3)   // "lo"

"hello".chopSuffix()    // "hell"
"hello".chopSuffix(3)   // "he"

Like dropFirst and dropLast before them, these functions will crash if there aren't enough letters available in the String. The onus is on the caller to use them properly. This is a valid design decision. One could write them to return an optional which then would have to be unwrapped by the caller.

Swift 2.x

Alas in Swift 2, dropFirst and dropLast (the previous best solution) aren't as convenient as they were before. With an extension to String, you can hide the ugliness of substringFromIndex and substringToIndex:

extension String {
    func chopPrefix(count: Int = 1) -> String {
         return self.substringFromIndex(advance(self.startIndex, count))
    }

    func chopSuffix(count: Int = 1) -> String {
        return self.substringToIndex(advance(self.endIndex, -count))
    }
}

"hello".chopPrefix()    // "ello"
"hello".chopPrefix(3)   // "lo"

"hello".chopSuffix()    // "hell"
"hello".chopSuffix(3)   // "he"

Like dropFirst and dropLast before them, these functions will crash if there aren't enough letters available in the String. The onus is on the caller to use them properly. This is a valid design decision. One could write them to return an optional which then would have to be unwrapped by the caller.

In Swift 1.2, you'll need to call chopPrefix like this:

"hello".chopPrefix(count: 3)  // "lo"

or you can add an underscore _ to the function definitions to suppress the parameter name:

extension String {
    func chopPrefix(_ count: Int = 1) -> String {
         return self.substringFromIndex(advance(self.startIndex, count))
    }

    func chopSuffix(_ count: Int = 1) -> String {
        return self.substringToIndex(advance(self.endIndex, -count))
    }
}

Upvotes: 160

Hardik Thakkar
Hardik Thakkar

Reputation: 15951

To remove first character from string

let choppedString = String(txtField.text!.characters.dropFirst())

Upvotes: 0

Mick MacCallum
Mick MacCallum

Reputation: 130193

If you're using Swift 3, you can ignore the second section of this answer. Good news is, this is now actually succinct again! Just using String's new remove(at:) method.

var myString = "Hello, World"
myString.remove(at: myString.startIndex)

myString // "ello, World"

I like the global dropFirst() function for this.

let original = "Hello" // Hello
let sliced = dropFirst(original) // ello

It's short, clear, and works for anything that conforms to the Sliceable protocol.

If you're using Swift 2, this answer has changed. You can still use dropFirst, but not without dropping the first character from your strings characters property and then converting the result back to a String. dropFirst has also become a method, not a function.

let original = "Hello" // Hello
let sliced = String(original.characters.dropFirst()) // ello

Another alternative is to use the suffix function to splice the string's UTF16View. Of course, this has to be converted back to a String afterwards as well.

let original = "Hello" // Hello
let sliced = String(suffix(original.utf16, original.utf16.count - 1)) // ello

All this is to say that the solution I originally provided has turned out not to be the most succinct way of doing this in newer versions of Swift. I recommend falling back on @chris' solution using removeAtIndex() if you're looking for a short and intuitive solution.

var original = "Hello" // Hello
let removedChar = original.removeAtIndex(original.startIndex)

original // ello

And as pointed out by @vacawama in the comments below, another option that doesn't modify the original String is to use substringFromIndex.

let original = "Hello" // Hello
let substring = original.substringFromIndex(advance(original.startIndex, 1)) // ello

Or if you happen to be looking to drop a character off the beginning and end of the String, you can use substringWithRange. Just be sure to guard against the condition when startIndex + n > endIndex - m.

let original = "Hello" // Hello

let newStartIndex = advance(original.startIndex, 1)
let newEndIndex = advance(original.endIndex, -1)

let substring = original.substringWithRange(newStartIndex..<newEndIndex) // ell

The last line can also be written using subscript notation.

let substring = original[newStartIndex..<newEndIndex]

Upvotes: 257

Andrew
Andrew

Reputation: 3969

"en_US,fr_CA,es_US".chopSuffix(5).chopPrefix(5) // ",fr_CA,"

extension String {
    func chopPrefix(count: Int = 1) -> String {
        return self.substringFromIndex(self.startIndex.advancedBy(count))
    }

    func chopSuffix(count: Int = 1) -> String {
        return self.substringToIndex(self.endIndex.advancedBy(-count))
    }
}

Upvotes: 1

jrc
jrc

Reputation: 21891

In Swift 2, do this:

let cleanedString = String(theString.characters.dropFirst())

I recommend https://www.mikeash.com/pyblog/friday-qa-2015-11-06-why-is-swifts-string-api-so-hard.html to get an understanding of Swift strings.

Upvotes: 12

ChikabuZ
ChikabuZ

Reputation: 10185

In Swift 2 use this String extension:

extension String
{
    func substringFromIndex(index: Int) -> String
    {
        if (index < 0 || index > self.characters.count)
        {
            print("index \(index) out of bounds")
            return ""
        }
        return self.substringFromIndex(self.startIndex.advancedBy(index))
    }
}

display.text = display.text!.substringFromIndex(1)

Upvotes: 1

Gregory Higley
Gregory Higley

Reputation: 16558

I know of nothing more succinct out of the box, but you could easily implement prefix ++, e.g.,

public prefix func ++ <I: ForwardIndexType>(index: I) -> I {
    return advance(index, 1)
}

After which you can use it to your heart's content very succinctly:

str.substringFromIndex(++str.startIndex)

Upvotes: 1

chris
chris

Reputation: 4996

What about this?

s.removeAtIndex(s.startIndex)

This of course assumes that your string is mutable. It returns the character which has been removed, but alters the original string.

Upvotes: 6

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