First words

First words can be used to summarize text. They can generate a summary from a string that is much shorter than the entire string.

This logic is useful for summaries and captions. We examine a C# method that counts words and returns the first words.

Input and output

Suppose we have a phrase like "the bird is blue." We can take only the first 2 words from this phrase, leaving us with "the bird" only.

Input:    The bird is blue
Words(2): The bird

Example

We avoid all string copying except one Substring. We count spaces as we go over the string. When the number of spaces equals the number of words, we return the Substring.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

class Program
{
    static void Main()
    {
        Console.WriteLine(FirstWords("The bird is blue", 2));
        Console.WriteLine(FirstWords("This sentence has many words.", 4));
    }

    /// <summary>
    /// Get the first several words from the summary.
    /// </summary>
    public static string FirstWords(string input, int numberWords)
    {
        // Number of words we still want to display.
        int words = numberWords;
        // Loop through entire summary.
        for (int i = 0; i < input.Length; i++)
        {
            // Increment words on a space.
            if (input[i] == ' ')
            {
                words--;
            }
            // If we have no more words to display, return the substring.
            if (words == 0)
            {
                return input.Substring(0, i);
            }
        }
        return string.Empty;
    }
}
The bird
This sentence has many

Notes, performance

Speed here is good because only one string copy is made. All we are doing here is counting spaces and returning a substring.

We extracted the first several words from a sentence. Use this C# method and adapt it to your precise needs to extract the first words from a string.