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 ));

It's much simpler than all that:

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

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

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 (" ");

Use the regex pattern

    [ ]+    #only space

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

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) "

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;
        }
    }

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();