How can I find all indexes of a pattern in a string using c#?
For example I want to find all ## pattern indexes in a string like this 45##78$$#56$$JK01UU
- How do you define a "pattern"?Cheng Chen– Cheng Chen2012-05-11 06:15:19 +00:00Commented May 11, 2012 at 6:15
- Have you tried anything? Have you tried Regular Expressions?SCB– SCB2012-05-11 06:15:22 +00:00Commented May 11, 2012 at 6:15
- 1Could you show some input strings and intended output ?Habib– Habib2012-05-11 06:15:34 +00:00Commented May 11, 2012 at 6:15
- input pattern is ## string is 45##78$$#56$$JK01UUsanchop22– sanchop222012-05-11 06:15:57 +00:00Commented May 11, 2012 at 6:15
- string SearchPattern = "##"; string Str = "45##78$$#56$$JK01UU";sanchop22– sanchop222012-05-11 06:17:08 +00:00Commented May 11, 2012 at 6:17
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5 Answers
string pattern = "##"; string sentence = "45##78$$#56$$J##K01UU"; IList<int> indeces = new List<int>(); foreach (Match match in Regex.Matches(sentence, pattern)) { indeces.Add(match.Index); } indeces will have 2, 14
answered May 11, 2012 at 6:40
Prashanth Thurairatnam
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1 Comment
WtFudgE
or in 1 line: var indexes = Regex.Matches(_msg, pattern).Select(x => x.Index).ToList();
Edited the code to make it a cleaner function.
public IEnumerable<int> FindAllIndexes(string str, string pattern) { int prevIndex = -pattern.Length; // so we start at index 0 int index; while((index = str.IndexOf(pattern, prevIndex + pattern.Length)) != -1) { prevIndex = index; yield return index; } } string str = "45##78$$#56$$JK01UU"; string pattern = "##"; var indexes = FindAllIndexes(str, pattern); 
1 Comment
mortb
I guess this must be faster than the answers that use regex. Would be nice to have some profiling results.
You can get all the indices of a pattern in a string by using a regex search like this.
string input = "45##78$$#56$$JK01UU", pattern = Regex.Escape("##"); Regex rx = new Regex(pattern); var indices = new List<int>(); var matches = rx.Matches(s); for (int i=0 ; i<matches.Length ; i++) { indices.Add(matches[i].Index); } 
1 Comment
yamen
You probably need to run
Regex.Escape() on the pattern.Another one that tries to be efficient:
public IEnumerable<int> FindPatternIndexes(string input, string search) { var sb = new StringBuilder(input); for (var i = 0; search.Length <= sb.Length; i++) { if (sb.ToString().StartsWith(search)) yield return i; sb.Remove(0,1); } } Comments
Tested. Worked. But somewhat dumb.
string foo = "45##78$$#56$$JK01UU"; char[] fooChar = foo.ToCharArray(); int i = 0; bool register = false; foreach (char fc in fooChar) { if (fc == '#' && register == true) { MessageBox.Show("Index: " + (i-1)); } else if (fc == '#') { register = true; } else { register = false; } i++; } 