How to count specific string using regex

Question

I'm a newbie of using regex.

How can I count specific letter on a string ?

var str = "FFFF000FFFCA";

i want an output of 4F303FCA.

I used Regex.Replace(str, @"(.)\1*", m => m.Value.Length + m.Groups[1].Value); but the output is : 4F303F1C1A

Thank you for helping.

That output looks right to me.

Sam Axe
– Sam Axe

2015-03-24 02:05:39 +00:00
Commented Mar 24, 2015 at 2:05 — Sam Axe
– Sam Axe, Commented Mar 24, 2015 at 2:05

Alexei Levenkov · Accepted Answer · 2015-03-24 02:21:20Z

1

Looks like you want to output nothing when there is only one occurrence. You can use "conditional operator" (aka "ternary") to make that choice inline:

string input = "FFFF000FFFCA";
string output = Regex.Replace(input, 
    @"(.)\1*", m => 1 < m.Value.Length ? 
           m.Value.Length.ToString() + m.Groups[1].Value : m.Groups[1].Value);

Note something like 21 could not be decoded back (assuming you are trying to implement version of Run-length encoding).

edited Mar 24, 2015 at 2:21

Alexei Levenkov

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answered Mar 24, 2015 at 2:09

Sam Axe

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2 Comments

Alexei Levenkov Over a year ago

I've added some water to your post so it is not such a dry code sample... Feel free to revert.

Marc Corpuz Nacionales Over a year ago

Thank you. That's what i want. What if specific letter? Only letter "F". Output is : 4F0003FCA. thanks alot.

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