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

I like to use:

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

Since it will catch runs of any kind of whitespace (e.g. tabs, newlines, etc.) and replace them with a single space.

string sentence = "This is a sentence with multiple    spaces";
RegexOptions options = RegexOptions.None;
Regex regex = new Regex("[ ]{2,}", options);     
sentence = regex.Replace(sentence, " ");

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

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);

Another approach which uses LINQ:

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

It's much simpler than all that:

while(str.Contains("  ")) str = str.Replace("  ", " ");

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."

myString = Regex.Replace(myString, " {2,}", " ");

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.

This is a shorter version, which should only be used if you are only doing this once, as it creates a new instance of the Regex class every time it is called.

temp = new Regex(" {2,}").Replace(temp, " "); 

If you are not too acquainted with regular expressions, here's a short explanation:

The {2,} makes the regex search for the character preceding it, and finds substrings between 2 and unlimited times.
The .Replace(temp, " ") replaces all matches in the string temp with a space.

If you want to use this multiple times, here is a better option, as it creates the regex IL at compile time:

Regex singleSpacify = new Regex(" {2,}", RegexOptions.Compiled);
temp = singleSpacify.Replace(temp, " ");

You can simply do this in one line solution!

string s = "welcome to  london";
s.Replace(" ", "()").Replace(")(", "").Replace("()", " ");

You can choose other brackets (or even other characters) if you like.

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"

// Mysample string
string str ="hi you           are          a demo";

//Split the words based on white sapce
var demo= str .Split(' ').Where(s => !string.IsNullOrWhiteSpace(s));
        
//Join the values back and add a single space in between
str = string.Join(" ", demo);
// output: string str ="hi you are a demo";

Consolodating other answers, per Joel, and hopefully improving slightly as I go:

You can do this with Regex.Replace():

string s = Regex.Replace (
    "   1  2    4 5", 
    @"[ ]{2,}", 
    " "
    );

Or with String.Split():

static class StringExtensions
{
    public static string Join(this IList<string> value, string separator)
    {
        return string.Join(separator, value.ToArray());
    }
}

//...

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

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 (" ");

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();
    }

}

Use the regex pattern

    [ ]+    #only space

   var text = Regex.Replace(inputString, @"[ ]+", " ");

I know this is pretty old, but ran across this while trying to accomplish almost the same thing. Found this solution in RegEx Buddy. This pattern will replace all double spaces with single spaces and also trim leading and trailing spaces.

pattern: (?m:^ +| +$|( ){2,})
replacement: $1

Its a little difficult to read since we're dealing with empty space, so here it is again with the "spaces" replaced with a "_".

pattern: (?m:^_+|_+$|(_){2,})  <-- don't use this, just for illustration.

The "(?m:" construct enables the "multi-line" option. I generally like to include whatever options I can within the pattern itself so it is more self contained.

I can remove whitespaces with this

while word.contains("  ")  //double space
   word = word.Replace("  "," "); //replace double space by single space.
word = word.trim(); //to remove single whitespces from start & end.

Without using regular expressions:

while (myString.IndexOf("  ", StringComparison.CurrentCulture) != -1)
{
    myString = myString.Replace("  ", " ");
}

OK to use on short strings, but will perform badly on long strings with lots of spaces.

try this method

private string removeNestedWhitespaces(char[] st)
{
    StringBuilder sb = new StringBuilder();
    int indx = 0, length = st.Length;
    while (indx < length)
    {
        sb.Append(st[indx]);
        indx++;
        while (indx < length && st[indx] == ' ')
            indx++;
        if(sb.Length > 1  && sb[0] != ' ')
            sb.Append(' ');
    }
    return sb.ToString();
}

use it like this:

string test = removeNestedWhitespaces("1 2 3  4    5".toCharArray());

Here is a slight modification on Nolonar original answer.

Checking if the character is not just a space, but any whitespace, use this:

It will replace any multiple whitespace character with a single space.

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

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

How about going rogue?

public static string MinimizeWhiteSpace(
    this string _this)
    {
        if (_this != null)
        {
            var returned = new StringBuilder();
            var inWhiteSpace = false;
            var length = _this.Length;
            for (int i = 0; i < length; i++)
            {
                var character = _this[i];
                if (char.IsWhiteSpace(character))
                {
                    if (!inWhiteSpace)
                    {
                        inWhiteSpace = true;
                        returned.Append(' ');
                    }
                }
                else
                {
                    inWhiteSpace = false;
                    returned.Append(character);
                }
            }
            return returned.ToString();
        }
        else
        {
            return null;
        }
    }

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 CondenseSpaces(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()
    {
        const string input = "     (five leading spaces)     (five internal spaces)     (five trailing spaces)     ";
        
        Console.WriteLine(" Input: \"{0}\"", input);
        Console.WriteLine("Output: \"{0}\"", StringExtension.CondenseSpaces(input));
    }
}

Executing this program produces the following output:

 Input: "     (five leading spaces)     (five internal spaces)     (five trailing spaces)     "
Output: " (five leading spaces) (five internal spaces) (five trailing spaces) "

Old skool:

string oldText = "   1 2  3   4    5     ";
string newText = oldText
                    .Replace("  ", " " + (char)22 )
                    .Replace( (char)22 + " ", "" )
                    .Replace( (char)22 + "", "" );

Assert.That( newText, Is.EqualTo( " 1 2 3 4 5 " ) );

I looked over proposed solutions, could not find the one that would handle mix of white space characters acceptable for my case, for example:

Regex.Replace(input, @"\s+", " ") - it will eat your line breaks, if they are mixed with spaces, for example \n \n sequence will be replaced with

Regex.Replace(source, @"(\s)\s+", "$1") - it will depend on whitespace first character, meaning that it again might eat your line breaks

Regex.Replace(source, @"[ ]{2,}", " ") - it won't work correctly when there's mix of whitespace characters - for example "\t \t "

Probably not perfect, but quick solution for me was:

Regex.Replace(input, @"\s+", 
(match) => match.Value.IndexOf('\n') > -1 ? "\n" : " ", RegexOptions.Multiline)

Idea is - line break wins over the spaces and tabs.

This won't handle windows line breaks correctly, but it would be easy to adjust to work with that too, don't know regex that well - may be it is possible to fit into single pattern.

The following code remove all the multiple spaces into a single space

    public string RemoveMultipleSpacesToSingle(string str)
    {
        string text = str;
        do
        {
            //text = text.Replace("  ", " ");
            text = Regex.Replace(text, @"\s+", " ");
        } while (text.Contains("  "));
        return text;
    }

You can create a StringsExtensions file with a method like RemoveDoubleSpaces().

StringsExtensions.cs

public static string RemoveDoubleSpaces(this string value)  
{
  Regex regex = new Regex("[ ]{2,}", RegexOptions.None);
  value = regex.Replace(value, " ");

  // this removes space at the end of the value (like "demo ")
  // and space at the start of the value (like " hi")
  value = value.Trim(' ');

  return value;
}

And then you can use it like this:

string stringInput =" hi here     is  a demo ";

string stringCleaned = stringInput.RemoveDoubleSpaces();