How do I replace multiple spaces with a single space in C#?

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

Regex can be rather slow even with simple tasks. This creates an extension method that can be used off of any string.

    public static class StringExtension
    {
        public static String ReduceWhitespace(this String value)
        {
            var newString = new StringBuilder();
            bool previousIsWhitespace = false;
            for (int i = 0; i < value.Length; i++)
            {
                if (Char.IsWhiteSpace(value[i]))
                {
                    if (previousIsWhitespace)
                    {
                        continue;
                    }

                    previousIsWhitespace = true;
                }
                else
                {
                    previousIsWhitespace = false;
                }

                newString.Append(value[i]);
            }

            return newString.ToString();
        }
    }

It would be used as such:

string testValue = "This contains     too          much  whitespace."
testValue = testValue.ReduceWhitespace();
// testValue = "This contains too much whitespace."

Answer 3

no Regex, no Linq... removes leading and trailing spaces as well as reducing any embedded multiple space segments to one space

string myString = "   0 1 2  3   4               5  ";
myString = string.Join(" ", myString.Split(new char[] { ' ' }, 
StringSplitOptions.RemoveEmptyEntries));

result:"0 1 2 3 4 5"

Answer 4

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 5

I just wrote a new Join that I like, so I thought I'd re-answer, with it:

public static string Join<T>(this IEnumerable<T> source, string separator)
{
    return string.Join(separator, source.Select(e => e.ToString()).ToArray());
}

One of the cool things about this is that it work with collections that aren't strings, by calling ToString() on the elements. Usage is still the same:

//...

string s = "     1  2    4 5".Split (
    " ".ToCharArray(), 
    StringSplitOptions.RemoveEmptyEntries
    ).Join (" ");

Answer 6

Another approach which uses LINQ:

 var list = str.Split(' ').Where(s => !string.IsNullOrWhiteSpace(s));
 str = string.Join(" ", list);