Question

For example I have an input: "Test your Internet connection bandwidth. Test your Internet connection bandwidth." (two times repeated) and I want to search for strings internet and bandwidth.

string keyword = tbSearch.Text //That holds value: "internet bandwidth"
string input = "Test your Internet connection bandwidth. Test your Internet connection bandwidth.";

Regex r = new Regex(keyword.Replace(' ', '|'), RegexOptions.IgnoreCase);
if (r.Matches(input).Count == siteKeyword.Split(' ').Length)
{
    //Do something
}

This doesn’t work cause it finds 2 “internet” and 2 “bandwidth”, so it count 4 but the keyword length is 2. So what I can do?

Answer 1

var pattern = keyword.Split()
        .Aggregate(new StringBuilder(),
                   (sb, s) => sb.AppendFormat(@"(?=.*\b{0}\b)", Regex.Escape(s)),
                   sb => sb.ToString());

if (Regex.IsMatch(input, pattern, RegexOptions.IgnoreCase))
{
    // contains all keywords
}

First part is generating pattern from your keywords. If there is two keywords "internet bandwidth", then generated regex pattern will look like:

"(?=.*\binternet\b)(?=.*\bbandwidth\b)"

It will match following inputs:

"Test your Internet connection bandwidth."
"Test your Internet connection bandwidth. Test your Internet bandwidth."

Following inputs will not match (not all words contained):

"Test your Internet2 connection bandwidth bandwidth."
"Test your connection bandwidth."

---

Another option (verifying each keyword separately):

var allWordsContained = keyword.Split().All(word => 
    Regex.IsMatch(input, String.Format(@"\b{0}\b", Regex.Escape(word)), RegexOptions.IgnoreCase));