I want to replace n occurrence of a substring in a string.

myString = "I have a mobile. I have a cat.";

How I can replace the second have of myString

CodePudding user response：

Something like that should work:

String replaceNthOccurrence(String input, int n, String from, String to) {
  var index = -1;
  
  while (--n >= 0) {
    index = input.indexOf(from,   index);
    if (index == -1) {
      break;
    }
  }
  
  if (index != -1) {
    var result = input.replaceFirst(from, to, index);
    return result;
  }
  
  return input;
} 

void main() {
   var myString = "I have a mobile. I have a cat.";
   var replacedString = replaceNthOccurrence(myString, 2, "have", "had");
   print(replacedString); // prints "I have a mobile. I had a cat."
}

CodePudding user response：

let's try with this

void main() {
  var myString = "I have a mobile. I have a cat.I have a cat";
  print(replaceInNthOccurrence(myString, "have", "test", 1));
}

String replaceInNthOccurrence(
    String stringToChange, String searchingWord, String replacingWord, int n) {
  if(n==1){
    return stringToChange.replaceFirst(searchingWord, replacingWord);
  }
  final String separator = "#######";
  
  String splittingString =
      stringToChange.replaceAll(searchingWord, separator   searchingWord);
  var splitArray = splittingString.split(separator);
  print(splitArray);
  String result = "";
  for (int i = 0; i < splitArray.length; i  ) {
    if (i % n == 0) {
      splitArray[i] = splitArray[i].replaceAll(searchingWord, replacingWord);
    }
    result  = splitArray[i];
  }
  return result;
}

CodePudding user response：

hope this simple function helps. You can also extract the function contents if you don't wish a function. It's just two lines with some Dart magic

void main() {
  String myString = 'I have a mobile. I have a cat.';
  String searchFor='have';
  int replaceOn = 2;
  String replaceText = 'newhave';
  String result = customReplace(myString,searchFor,replaceOn,replaceText);
  print(result);
}

String customReplace(String text,String searchText, int replaceOn, String replaceText){
  Match result = searchText.allMatches(text).elementAt(replaceOn - 1);
  return text.replaceRange(result.start,result.end,replaceText);
}

CodePudding user response：

This would be a better solution to undertake as it check the fallbacks also. Let me list down all the scenarios:

1. If position is 0 then it will replace all occurrence.
2. If position is correct then it will replace at same location.
3. If position is wrong then it will send back input string.
4. If substring does not exist in input then it will send back input string.

void main() {
          String input = "I have a mobile. I have a cat.";
          print(replacenth(input, 'have', 'need', 1));
        }
        
        /// Computes the nth string replace.
        String replacenth(String input, String substr, String replstr,int position) {
          
          if(input.contains(substr))
          {
            var splittedStr = input.split(substr);
            if(splittedStr.length == 0)
              return input;
              
            String finalStr = "";
            
            for(int i = 0; i < splittedStr.length; i  )
            {
              finalStr  = splittedStr[i];
              if(i == (position - 1))
                finalStr  = replstr;
              else if(i < (splittedStr.length - 1))
                finalStr  = substr;
            }
            
            return finalStr;
          }
          
          return input;
        }