First words

Sometimes it is necessary to have a function that gets only the first several words in a string. This can be helpful for user interfaces.

With Swift, we can count the first words, and return a new string containing just those words. We must take a substring for this function.

Example

To begin, we introduce the firstWords function. This receives a String containing the original text, and an integer that indicates the desired number of words.

Step 1 We loop over the source string with the enumerated() function, which returns indexes and characters.

Step 2 We detect space characters. When a space is encountered, we reduce the remaining words count.

Step 3 Here compute the string range by using startIndex and the index() function. We return a String based on that substring.

Step 4 If the number of words specified was more than the number of spaces in the string, we just return the original.

func firstWords(source: String, count: Int) -> String {
    var words = count
    // Step 1: use enumerated over string.
    for (i, c) in source.enumerated() {
        // Step 2: check for space, and decrement words count.
        if c == " " {
            words -= 1
            if words == 0 {
                // Step 3: get range for substring and return it.
                let r = source.startIndex..<source.index(source.startIndex, offsetBy: i)
                return String(source[r])
            }
        }
    }
    // Step 4: return original string.
    return source
}

let value = "there are many reasons"

// Test the first words method.
let result1 = firstWords(source: value, count: 2)
print(result1)

let result2 = firstWords(source: value, count: 3)
print(result2)

let result3 = firstWords(source: value, count: 100)
print(result3)there are
there are many
there are many reasons

With Swift it is possible to develop simple char-counting methods that return substrings. The code is clear and reliable, and can be extended for more complex purposes.