Need help using regex function/trimming my string-CodePudding

I have been stuck on this for a bit now, my output looks as follows: the first 2 letters represents the hallway number, so 17 for the first one, and the following number represents the shelf number, (location in hallway). As you can see in hallway 17 shelf 1 we have either A1 or A, but that doesn't matter. I want the output for 171A1 to be 171, and for 15211 to be 1521, so I want to remove the alphabetic letters at the end combined with the numbers which may follow after.

I tried using string.Remove(string.Length-2) but this doesn't work as we have 171A for example, which should become 171. Any help would be appreciated.

CodePudding user response：

In case you don't need it to be REGEX, this should work

var rawString = "15211";
var maxLength = 4;
var trimmedResult = new string(
        rawString.TakeWhile(char.IsNumber) // loop through characters using LINQ. since your string starts with numbers, you can just keep taking until you bump into a character
            .Take(maxLength) // limit the length for cases like "15211" where you don't need the extra numbers in the end
            .ToArray() // so we can use the new string() constructor
        );

CodePudding user response：

For the part in the question, you can use a pattern with a capture group, and use the group in the replacement:

^([0-9]{2,}?)[A-Z]?[0-9]?$

^ Start of string
([0-9]{2,}?) Capture group 1, match 2 digits 0-9 non greedy
[A-Z]?[0-9]? Match an optional char A-Z and optional digit 0-9
$ End of string

See a regex demo.

string pattern = @"^([0-9]{2,}?)[A-Z]?[0-9]?$";
string[] strings = { "171A1", "171A1", "171A", "171A0", "15211", "15211", "15211", "15210", "15190" };
foreach (String s in strings)
{
    Console.WriteLine(Regex.Replace(s, pattern, "$1"));
}

Output

If you want to separate the output by a dot after the 2 digits, you can use 2 capture groups and match at least 1 or more digits in the second group:

string pattern = @"^([0-9]{2})([0-9] ?)[A-Z]?[0-9]?$";
string[] strings = { "171A1", "171A1", "171A", "171A0", "15211", "15211", "15211", "15210", "15190" };
foreach (String s in strings)
{
    Console.WriteLine(Regex.Replace(s, pattern, "$1.$2"));
}

Output

See a C# demo