How to completely discard the occurrence of a string not matching the regex pattern?

Question

I am implementing a regex pattern to a list of strings. Example of such a string is: "MNT-PUT-Y0-HAS90" . There are other UNWANTED strings as well, like: "MNT-PUT-HAS90" .

When I execute the below code, I get "" for the unwanted one, which I guess how Regex works. And, I get "MNT-PUT-Y0-HAS90" for the wanted one.

The question is: How can I completely ignore the occurrence of MNT-PUT-HAS90. I want to retrieve results for string - "MNT-PUT-Y0-HAS90" only.

I have implemented the below code for this:

Store = a.Type == "Machines" ? 
string.Join(",", a.Info.Disk.Select(b => b.Store).
Select(x => Regex.Match(x, "[A-Z]+-[A-Z]+-T[0-9]-[A-Z]+[0-9]"))) : null

I tried changing the code to the below, but it shows me an error: "Cannot convert lambda expression to the intended delegate type because some of the return types in the block are not implicitly convertible to the delegate return type"

Store = a.Type == "Machines" ? 
    string.Join(",", a.Info.Disk.Select(b => b.Store).
    Where(x => Regex.Match(x, "[A-Z]+-[A-Z]+-T[0-9]-[A-Z]+[0-9]")).ToString()) : null

EDIT: Just tried this:

Store = a.Type == "Machines" ? 
        string.Join(",", a.Info.Disk.Select(b => b.Store).
        Where(x => Regex.IsMatch(x, "[A-Z]+-[A-Z]+-T[0-9]-[A-Z]+[0-9]")).ToList()) : null

I get no error but do not get the desired output either.

Answer 1

You need to use

Regex.IsMatch(x, "^[A-Z]+-[A-Z]+-[A-Z]+[0-9]+-[A-Z]+[0-9]+$")

See how this regex works .

Details

• ^ - start of the string
• [AZ]+ - 1+ ASCII uppercase letters
• - - a hypehn
• [AZ]+- - - 1+ ASCII uppercase letters and a hyphen
• [AZ]+[0-9]+- - 1+ ASCII uppercase letters, 1+ ASCII digits and then a hyphen
• [AZ]+[0-9]+ - 1+ ASCII uppercase letters, 1+ ASCII digits
• $ - end of string.

Code:

Store = a.Type == "Machines" ? 
    string.Join(",", 
        a.Info.Disk
           .Select(b => b.Store)
           .Where(x => Regex.IsMatch(x, "^[A-Z]+-[A-Z]+-[A-Z]+[0-9]+-[A-Z]+[0-9]+$"))
    ) 
    : null;

If the match is expected anywhere inside a longer string, remove ^ and $ anchors.

Answer 2

It was a very easy solution to it but somehow I was missing it... I did the below to resolve the issue:

Store = a.Type == "Machines" && a.Power == "on" && 
       string.Join(",", a.Info.Disk.Select(b => b.Store).
       Where(x => Regex.Match(x, "[A-Z]+-[A-Z]+-T[0-9]-[A-Z]+[0-9]"))) != "" ?
       "Do your stuff" : null