c# - Removing whitespace between consecutive numbers

Question

I have a string, from which I want to remove the whitespaces between the numbers:

string test = "Some Words 1 2 3 4";
string result = Regex.Replace(test, @"(d)s(d)", @"$1$2");

the expected/desired result would be:

"Some Words 1234"

but I retrieve the following:

"Some Words 12 34"

What am I doing wrong here?

Further examples:

Input:  "Some Words That Should not be replaced 12 9 123 4 12"
Output: "Some Words That Should not be replaced 129123412"

Input:  "test 9 8"
Output: "test 98"

Input:  "t e s t 9 8"
Output: "t e s t 98"

Input:  "Another 12 000"
Output: "Another 12000"

Answer 1

Regex.Replace continues to search after the previous match:

Some Words 1 2 3 4
           ^^^
         first match, replace by "12"

Some Words 12 3 4
             ^
             +-- continue searching here

Some Words 12 3 4
              ^^^
            next match, replace by "34"

You can use a zero-width positive lookahead assertion to avoid that:

string result = Regex.Replace(test, @"(d)s(?=d)", @"$1");

Now the final digit is not part of the match:

Some Words 1 2 3 4
           ^^?
         first match, replace by "1"

Some Words 12 3 4
            ^
            +-- continue searching here

Some Words 12 3 4
            ^^?
            next match, replace by "2"

...