How would you count occurences of a string within a string (C#)?

Question

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 about 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?

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

Answer 1

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.

Answer 2

LINQ works on all collections, and since strings are just a collection of characters, how about this nice little one-liner:

var count = source.Count(c => c == '/');

Answer 3

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.)

Answer 4

These both only work for single-character search terms...

countOccurences("the", "the answer is the answer");

int countOccurences(string needle, string haystack)
{
    return (haystack.Length - haystack.Replace(needle,"").Length) / needle.Length;
}

may turn out to be better for longer needles...

But there has to be a more elegant way. :)

Answer 5

If you want to be able to search for whole strings, and not just characters:

src.Select((c, i) => src.Substring(i)).Count(sub => sub.StartsWith(target))

Read as "for each character in the string, take the rest of the string starting from that character as a substring; count it if it starts with the target string."

Answer 6

source.Split('/').Count - 1

Answer 7

I like your original solution better than any of the other ways.

Answer 8

source.Length - (source.Length - source.Trim('/').Length);

Not working :0 Sorry