Replace the last occurrence of a word in a string - C#

Question

I have a problem where I need to replace the last occurrence of a word in a string.

Situation: I am given a string which is in this format:

Answer 1

Here is the function to replace the last occurrence of a string

public static string ReplaceLastOccurrence(string Source, string Find, string Replace)
{
        int place = Source.LastIndexOf(Find);

        if(place == -1)
           return Source;

        string result = Source.Remove(place, Find.Length).Insert(place, Replace);
        return result;
}

• Source is the string on which you want to do the operation.
• Find is the string that you want to replace.
• Replace is the string that you want to replace it with.

Answer 2

You have to do the replace manually:

int i = filePath.LastIndexOf(TnaName);
if (i >= 0)
    filePath = filePath.Substring(0, i) + filePath.Substring(i + TnaName.Length);

Answer 3

Use string.LastIndexOf() to find the index of the last occurrence of the string and then use substring to look for your solution.

Answer 4

var lastIndex = filePath.LastIndexOf(TnaName);

filePath = filePath.Substring(0, lastIndex);

Answer 5

The solution can be implemented even more simple with a single line:

 static string ReplaceLastOccurrence(string str, string toReplace, string replacement)
    {
        return Regex.Replace(str, $@"^(.*){toReplace}(.*?)$", $"$1{replacement}$2");
    }

Hereby we take advantage of the greediness of the regex asterisk operator. The function is used like this:

var s = "F:/feb11/MFrame/Templates/feb11";
var tnaName = "feb11";
var r = ReplaceLastOccurrence(s,tnaName, string.Empty);

Answer 6

I don't see why Regex can't be used:

public static string RegexReplace(this string source, string pattern, string replacement)
{
  return Regex.Replace(source,pattern, replacement);
}

public static string ReplaceEnd(this string source, string value, string replacement)
{
  return RegexReplace(source, $"{value}$", replacement);
}

public static string RemoveEnd(this string source, string value)
{
  return ReplaceEnd(source, value, string.Empty);
}

Usage:

string filePath ="F:/feb11/MFrame/Templates/feb11";
filePath = filePath.RemoveEnd("feb11"); // F:/feb11/MFrame/Templates/
filePath = filePath.ReplaceEnd("feb11","jan11"); // F:/feb11/MFrame/Templates/jan11