StringReplace with conditionals

Questions
1

Hey all,
can anybody please help me out here?
Why does the following line not replace every character that appears more than once in the string?

str = "AAbCC";
StringReplace[str, c_ -> "X" /; StringCount[str, c] > 1]

Does anyone have a more elegant solution?
Still learning Mathematica, sorry…

Thank you and all the best
Timo

2

Got it.
Once you do it right, it works :wink:

StringReplace[str, c_ /; (StringCount[str, c] > 1) -> "X"]
3

Alternatively you can do it this way:

StringReplace[str, c_ ~~ c_ -> "XX"]
4

For anyone interested. Here’s my complete code. From time to time I try to solve exercises from codewars in different languages.

This one is based on this one Duplicate Encoder | Codewars

On[Assert];
singleEncode = "(";
doubleEncode = ")";
distinctChars = "ABCDE";
distinctCharsMixed = "AbCdE";
doubledChars = "AABBCCDDEE";
doubledCharsMixed = "AabBCcDdEe";

encodeString[s_String] := 
  StringReplace[
   s, {(c_ /; (StringCount[s, c, IgnoreCase -> True] > 1) -> 
      doubleEncode), (c_ -> singleEncode)}];

Assert[encodeString[distinctChars] == "((((("]
Assert[encodeString[distinctCharsMixed] == "((((("]
Assert[encodeString[doubledChars] == "))))))))))"]
Assert[encodeString[doubledCharsMixed] == "))))))))))"]
5

Thank you!