How would you count occurrences of a string (actually a char) within a string?


I am doing something where I realised I wanted to count how many /s I could find in a string, and then it struck me, that there were several ways to do it, but couldn't decide on what the best (or easiest) was.

At the moment I'm going with something like:

string source = "/once/upon/a/time/";
int count = source.Length - source.Replace("/", "").Length;

But I don't like it at all, any takers?

I don't really want to dig out RegEx for this, do I?

I know my string is going to have the term I'm searching for, so you can assume that...

Of course for strings where length > 1,

string haystack = "/once/upon/a/time";
string needle = "/";
int needleCount = ( haystack.Length - haystack.Replace(needle,"").Length ) / needle.Length;
4/24/2018 11:20:31 AM

Accepted Answer

If you're using .NET 3.5 you can do this in a one-liner with LINQ:

int count = source.Count(f => f == '/');

If you don't want to use LINQ you can do it with:

int count = source.Split('/').Length - 1;

You might be surprised to learn that your original technique seems to be about 30% faster than either of these! I've just done a quick benchmark with "/once/upon/a/time/" and the results are as follows:

Your original = 12s
source.Count = 19s
source.Split = 17s
foreach (from bobwienholt's answer) = 10s

(The times are for 50,000,000 iterations so you're unlikely to notice much difference in the real world.)

5/23/2017 12:03:02 PM

string source = "/once/upon/a/time/";
int count = 0;
foreach (char c in source) 
  if (c == '/') count++;

Has to be faster than the source.Replace() by itself.

Licensed under: CC-BY-SA with attribution
Not affiliated with: Stack Overflow