How to get number of matches from Regex.Replace

Question

I want to do a regex replace in C# dot net, and I want to know how many replacements were made. What is the best way?

The best I can do now is to look at the before/after to see if anything changed

var a = "gooodbaaad";
var b = Regex.Replace(a,"[oa]","x");
if (a != b) Debug.Write("changed");

but this seems rather indirect and not accurate in all cases.

This doesn't look like a Regex replace from the code. Nothing will ever happen with the code above. — James Harcourt, Jun 05 '15 at 17:34
You could create a `System.Text.RegularExpressions.Regex`, then call `yourRegex.Replace(string input, MatchEvaluator evaluator)` and have your evaluator keep a count. Edit: this is basically what @NicholasCarey suggests in his answer. — adv12, Jun 05 '15 at 17:41
Look [here](http://stackoverflow.com/questions/4994225/count-regex-replaces-c) — voytek, Jun 05 '15 at 17:43

score 5 · Answer 1 · answered Jun 05 '15 at 17:41

Try something like the following. It transforms all sequences of 1 or more word characters to the literal text {word} and counts the replacements. So, the source text

The quick brown fox jumped over the lazy dog.

would be transformed to

{word} {word} {word} {word} {word} {word} {word} {word} {word}.

And at the end of the operation, the variable cnt has the value 9.

Regex pattern      = new Regex( @"\w+" ) ;
string source      = GetMeMySourceData() ;
int    cnt         = 0 ;
string transformed = pattern.Replace( source , m => {
    ++cnt ;
    return "{word}" ;
  });

The power of closures.

score 3 · Accepted Answer · answered Jun 05 '15 at 17:43

3

try to use another overload of Regex.Replace with MatchEvaluator

using System;
using System.Text.RegularExpressions;           

public class Program
{
    public static void Main()
    {
        int count = 0;
        var b = Regex.Replace("gooodbaaad", "[oa]", m=> { count++; return "x"; });

        Console.WriteLine(b);
        Console.WriteLine(count);           
    }
}

demo

answered Jun 05 '15 at 17:43

ASh

34,632
9
60
82

Thanks. It was not obvious to me from MSDN that I could use lambda in this context. Now I know! – John Henckel Jun 05 '15 at 17:56
@JohnHenckel, fine! `MatchEvaluator` is a delegate, so you can use a lambda expression – ASh Jun 05 '15 at 18:02
Technically your answer is not complete. You should have `return m.Result("x")` in case the string `"x"` contains `$1` or stuff like that. – John Henckel Jun 05 '15 at 18:31
@JohnHenckel, thank you for comment. i can't agree that it is not correct, since there are no captured groups here – ASh Jun 05 '15 at 18:41

How to get number of matches from Regex.Replace

2 Answers2