How do I replace multiple spaces with a single spa

Question

How can I replace multiple spaces in a string with only one space in C#?

Example:

1 2 3  4    5

would be:

1 2 3 4 5

Answer 1

Many answers are providing the right output but for those looking for the best performances, I did improve Nolanar's answer (which was the best answer for performance) by about 10%.

public static string MergeSpaces(this string str)
{

    if (str == null)
    {
        return null;
    }
    else
    {
        StringBuilder stringBuilder = new StringBuilder(str.Length);

        int i = 0;
        foreach (char c in str)
        {
            if (c != ' ' || i == 0 || str[i - 1] != ' ')
                stringBuilder.Append(c);
            i++;
        }
        return stringBuilder.ToString();
    }

}

Answer 2

Mix of StringBuilder and Enumerable.Aggregate() as extension method for strings:

using System;
using System.Linq;
using System.Text;

public static class StringExtension
{
    public static string StripSpaces(this string s)
    {
        return s.Aggregate(new StringBuilder(), (acc, c) =>
        {
            if (c != ' ' || acc.Length > 0 && acc[acc.Length-1] != ' ')
                acc.Append(c);

            return acc;
        }).ToString();
    }

    public static void Main()
    {
        Console.WriteLine("\"" + StringExtension.StripSpaces("1   Hello       World  2   ") + "\"");
    }
}

Input:

"1   Hello       World  2   "

Output:

"1 Hello World 2 "

Answer 3

I think Matt's answer is the best, but I don't believe it's quite right. If you want to replace newlines, you must use:

myString = Regex.Replace(myString, @"\s+", " ", RegexOptions.Multiline);

Answer 4

For those, who don't like Regex, here is a method that uses the StringBuilder:

    public static string FilterWhiteSpaces(string input)
    {
        if (input == null)
            return string.Empty;

        StringBuilder stringBuilder = new StringBuilder(input.Length);
        for (int i = 0; i < input.Length; i++)
        {
            char c = input[i];
            if (i == 0 || c != ' ' || (c == ' ' && input[i - 1] != ' '))
                stringBuilder.Append(c);
        }
        return stringBuilder.ToString();
    }

In my tests, this method was 16 times faster on average with a very large set of small-to-medium sized strings, compared to a static compiled Regex. Compared to a non-compiled or non-static Regex, this should be even faster.

Keep in mind, that it does not remove leading or trailing spaces, only multiple occurrences of such.