Question

I tried to replace   elements in a string using .NET regex – with no luck 🙂

Assume the following string:

 AA A  C D   A Some Text   here

The rules

1. Do not replace at beginning of line
2. Do only replace single occurrences
3. Do not replace if a space is before or after it (optional)

The desired result from above is (# as replacement character):

 AA#A  C#D   A#Some Text   here

Answer 1

This should cover all 3 of your requirements. Excuse the formatting; I had to back-tick the first few lines for the   to show up properly.

string pattern = @"(?<!^|&nbsp;)((?<!\s)&nbsp;(?!\s))(?!\1)";

string[] inputs = { " AA A  C D   A Some Text   here", // original

" AA A  C D   A  Some Text   here" // space before/after

};

foreach (string input in inputs)
{
    string result = Regex.Replace(input, pattern, "#");
    Console.WriteLine("Original: {0}\nResult: {1}", input, result);
}

Output:

Original:  AA A  C D   A Some Text   here

Result:  AA#A  C#D   A#Some Text   here

Original:  AA A  C D   A  Some Text   here

Result:  AA#A  C#D   A  Some Text   here