Removing numbers at the end of a string C#

Question

I'm trying to remove numbers in the end of a given string.

AB123 -> AB
123ABC79 -> 123ABC

I've tried something like this;

string input = "123ABC79";
string pattern = @"^\\d+|\\d+$";
string replacement = "";
Regex rgx = new Regex(pattern);
string result = rgx.Replace(input, replacement);

Yet the replacement string is same as the input. I'm not very familiar with regex. I can simply split the string into a character array, and loop over it to get it done, but it does not feel like a good solution. What is a good practice to remove numbers that are only in the end of a string?

Thanks in advance.

Answer 1

String.TrimEnd() is faster than using a regex:

var digits = new[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
var input = "123ABC79";
var result = input.TrimEnd(digits);

Benchmark app:

    string input = "123ABC79";
    string pattern = @"\d+$";
    string replacement = "";
    Regex rgx = new Regex(pattern);

    var iterations = 1000000;
    var sw = Stopwatch.StartNew();
    for (int i = 0; i < iterations; i++)
    {
        rgx.Replace(input, replacement);
    }

    sw.Stop();
    Console.WriteLine("regex:\t{0}", sw.ElapsedTicks);

    var digits = new[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
    sw.Restart();
    for (int i = 0; i < iterations; i++)
    {
        input.TrimEnd(digits);
    }

    sw.Stop();
    Console.WriteLine("trim:\t{0}", sw.ElapsedTicks);

Result:

regex:  40052843
trim:   2000635

Answer 2

Try this:

string input = "123ABC79";
string pattern = @"\d+$";
string replacement = "";
Regex rgx = new Regex(pattern);
string result = rgx.Replace(input, replacement);

Putting the $ at the end will restrict searches to numeric substrings at the end. Then, since we are calling Regex.Replace, we need to pass in the replacement pattern as the second parameter.

Demo

Answer 3

try this:

string input = "123ABC79";
string pattern = @".+\D+(?=\d+)";
Match match = Regex.Match(input, pattern);
string result = match.Value;

but you also can use a simple cycle:

string input = "123ABC79";
int i = input.Length - 1;
for (; i > 0 && char.IsDigit(input[i - 1]); i--)
{}
string result = input.Remove(i);