Get the string up to a specific character

Question

var hello = \"hello, how are you?\"

var hello2 = \"hello, how are you @tom?\"

i want to delete every letter behind the @ sign.

result shou

Answer 1

Try regular expressions, they are much safer (if you know what you are doing...)

  let hello2 = "hello, how are you @tom, @my @next @victim?"

    let deletedStringsAfterAtSign = hello2.replacingOccurrences(of: "@\\w+", with: "", options: .regularExpression, range: nil)

    print(deletedStringsAfterAtSign)
    //prints "hello, how are you ,   ?"

And this code removes exactly what you need and leaves the characters after the strings clear, so you can see the , and ? still being there. :)

EDIT: what you asked in comments to this answer:

  let hello2 = "hello, how are you @tom, @my @next @victim?"

  if let elementIwannaAfterEveryAtSign = hello2.components(separatedBy: " @").last
  {
    let deletedStringsAfterAtSign = hello2.replacingOccurrences(of: "@\\w+", with: elementIwannaAfterEveryAtSign, options: .regularExpression, range: nil)
    print(deletedStringsAfterAtSign)
    //prints hello, how are you victim?, victim? victim? victim??
    }

Answer 2

Expanding on @appzYourLife answer, the following will also trim off the whitespace characters after removing everything after the @ symbol.

import Foundation

var str = "hello, how are you @tom"

if str.contains("@") {
    let endIndex = str.range(of: "@")!.lowerBound
    str = str.substring(to: endIndex).trimmingCharacters(in: .whitespacesAndNewlines)
}
print(str) // Output - "hello, how are you"

UPDATE:

In response to finding the last occurance of the @ symbol in the string and removing it, here is how I would approach it:

var str = "hello, how are you @tom @tim?"
if str.contains("@") {
    //Reverse the string
    var reversedStr = String(str.characters.reversed())
    //Find the first (last) occurance of @
    let endIndex = reversedStr.range(of: "@")!.upperBound
    //Get the string up to and after the @ symbol
    let newStr = reversedStr.substring(from: endIndex).trimmingCharacters(in: .whitespacesAndNewlines)

    //Store the new string over the original
    str = String(newStr.characters.reversed())
    //str = "hello, how are you @tom"
}

Or looking at @appzYourLife answer use range(of:options:range:locale:) instead of literally reversing the characters

var str = "hello, how are you @tom @tim?"
if str.contains("@") {
    //Find the last occurrence of @
    let endIndex = str.range(of: "@", options: .backwards, range: nil, locale: nil)!.lowerBound
    //Get the string up to and after the @ symbol
    let newStr = str.substring(from: endIndex).trimmingCharacters(in: .whitespacesAndNewlines)

    //Store the new string over the original
    str = newStr
    //str = "hello, how are you @tom"
}

As an added bonus, here is how I would approach removing every @ starting with the last and working forward:

var str = "hello, how are you @tom and @tim?"
if str.contains("@") {

    while str.contains("@") {
        //Reverse the string
        var reversedStr = String(str.characters.reversed())
        //Find the first (last) occurance of @
        let endIndex = reversedStr.range(of: "@")!.upperBound
        //Get the string up to and after the @ symbol
        let newStr = reversedStr.substring(from: endIndex).trimmingCharacters(in: .whitespacesAndNewlines)

        //Store the new string over the original
        str = String(newStr.characters.reversed())
    }
    //after while loop, str = "hello, how are you"
}

Answer 3

You need to find the range of the "@" and then use it to create a substring up to the index before.

import Foundation

let text = "hello, how are you @tom?"

if let range = text.range(of: "@") {
    let result = text.substring(to: range.lowerBound)
    print(result) // "hello, how are you "
}

Considerations

Please note that, following the logic you described and using the input text you provided, the output string will have a blank space as last character

Also note that if multiple @ are presente in the input text, then the first occurrence will be used.

---

Last index [Update]

I am adding this new section to answer the question you posted in the comments.

If you have a text like this

let text = "hello @tom @mark @mathias"

and you want the index of the last occurrency of "@" you can write

if let index = text.range(of: "@", options: .backwards)?.lowerBound {
    print(index)    
}

Answer 4

let text = "hello, how are you @tom?"
let trimSpot = text.index(of: "@") ?? text.endIndex
let trimmed = text[..<trimSpot]

Since a string is a collection of Character type, it can be accessed as such. The second line finds the index of the @ sign and assigns its value to trimSpot, but if it is not there, the endIndex of the string is assigned through the use of the nil coalescing operator

    ??

The string, or collection of Characters, can be provided a range that will tell it what characters to get. The expression inside of the brackets,

    ..<trimSpot

is a range from 0 to trimSpot-1. So,

    text[..<trimSpot]

returns an instance of type Substring, which points at the original String instance.