C# - Simplest way to remove first occurrence of a substring from another string

Question

I need to remove the first (and ONLY the first) occurrence of a string from another string.

Here is an example replacing the string "\\Iteration". This:

ProjectName\\Iteration\\Release1\\Iteration1

would become this:

ProjectName\\Release1\\Iteration1

Here some code that does this:

const string removeString = "\\Iteration";
int index = sourceString.IndexOf(removeString);
int length = removeString.Length;
String startOfString = sourceString.Substring(0, index);
String endOfString = sourceString.Substring(index + length);
String cleanPath = startOfString + endOfString;

That seems like a lot of code.

So my question is this: Is there a cleaner/more readable/more concise way to do this?

Answer 1

int index = sourceString.IndexOf(removeString);
string cleanPath = (index < 0)
    ? sourceString
    : sourceString.Remove(index, removeString.Length);

Answer 2

You can replace all occurrences with Replace() given by removeString.

sourceString.Replace(removeString, "");

Answer 3

string myString = sourceString.Remove(sourceString.IndexOf(removeString),removeString.Length);

EDIT: @OregonGhost is right. I myself would break the script up with conditionals to check for such an occurence, but I was operating under the assumption that the strings were given to belong to each other by some requirement. It is possible that business-required exception handling rules are expected to catch this possibility. I myself would use a couple of extra lines to perform conditional checks and also to make it a little more readable for junior developers who may not take the time to read it thoroughly enough.

Answer 4

Wrote a quick TDD Test for this

    [TestMethod]
    public void Test()
    {
        var input = @"ProjectName\Iteration\Release1\Iteration1";
        var pattern = @"\\Iteration";

        var rgx = new Regex(pattern);
        var result = rgx.Replace(input, "", 1);
        
        Assert.IsTrue(result.Equals(@"ProjectName\Release1\Iteration1"));
    }

rgx.Replace(input, "", 1); says to look in input for anything matching the pattern, with "", 1 time.

Answer 5

You could use an extension method for fun. Typically I don't recommend attaching extension methods to such a general purpose class like string, but like I said this is fun. I borrowed @Luke's answer since there is no point in re-inventing the wheel.

[Test]
public void Should_remove_first_occurrance_of_string() {

    var source = "ProjectName\\Iteration\\Release1\\Iteration1";

    Assert.That(
        source.RemoveFirst("\\Iteration"),
        Is.EqualTo("ProjectName\\Release1\\Iteration1"));
}

public static class StringExtensions {
    public static string RemoveFirst(this string source, string remove) {
        int index = source.IndexOf(remove);
        return (index < 0)
            ? source
            : source.Remove(index, remove.Length);
    }
}

Answer 6

If you'd like a simple method to resolve this problem. (Can be used as an extension)

See below:

    public static string RemoveFirstInstanceOfString(this string value, string removeString)
    {
        int index = value.IndexOf(removeString, StringComparison.Ordinal);
        return index < 0 ? value : value.Remove(index, removeString.Length);
    }

Usage:

    string valueWithPipes = "| 1 | 2 | 3";
    string valueWithoutFirstpipe = valueWithPipes.RemoveFirstInstanceOfString("|");
    //Output, valueWithoutFirstpipe = " 1 | 2 | 3";

Inspired by and modified @LukeH's and @Mike's answer.

Don't forget the StringComparison.Ordinal to prevent issues with Culture settings. https://www.jetbrains.com/help/resharper/2018.2/StringIndexOfIsCultureSpecific.1.html

Answer 7

I definitely agree that this is perfect for an extension method, but I think it can be improved a bit.

public static string Remove(this string source, string remove,  int firstN)
    {
        if(firstN <= 0 || string.IsNullOrEmpty(source) || string.IsNullOrEmpty(remove))
        {
            return source;
        }
        int index = source.IndexOf(remove);
        return index < 0 ? source : source.Remove(index, remove.Length).Remove(remove, --firstN);
    }

This does a bit of recursion which is always fun.

Here is a simple unit test as well:

   [TestMethod()]
    public void RemoveTwiceTest()
    {
        string source = "look up look up look it up";
        string remove = "look";
        int firstN = 2;
        string expected = " up  up look it up";
        string actual;
        actual = source.Remove(remove, firstN);
        Assert.AreEqual(expected, actual);

    }