CODEWITHSUNDEEP
c#regexstringindexing
sanchop22
sanchop22

Reputation: 2809

Find all pattern indexes in string in C#

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

Upvotes: 5

Views: 15402

Answers (5)

jb.
jb.

Reputation: 10341

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);

Upvotes: 3

Prashanth Thurairatnam
Prashanth Thurairatnam

Reputation: 4361

 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

Upvotes: 9

KMC
KMC

Reputation: 20046

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++;
}

Upvotes: 0

McGarnagle
McGarnagle

Reputation: 102753

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);
}

Upvotes: 2

yamen
yamen

Reputation: 15618

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);
    }
}

Upvotes: 0

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