Question

How could I construct a LINQ expression to remove values from one list that meet the criteria of a function that returns a boolean?

string[] message = "days of the week"
message.ToList().RemoveAll(c=>checkShortWord(c));

public static bool checkShortWord(string word) {
       if ((word.Length > 3) &&                        
          (!Regex.IsMatch(word, "^[0-9]+$")))          
        return true;

      return false;
}

My ending string array should now be:

message = {"days","week"}

What should I change? My message array never changes.

Answer 1

You are constructing a new List and removing the items from that list, and then throwing it away. If you want an array that is missing the removed items, you will need to create a new one:

string[] message = "days of the week".Split(' ');
message = message.Where(c => checkShortWord(c)).ToArray();

Alternately, you could use a List<String> instead of a string[], and then use the RemoveAll method to modify it in place:

List<string> message = "days of the week".Split(' ').ToList();
message.RemoveAll(c => !checkShortWord(c));

As others have mentioned, you have also named your predicate method badly. “IsLongWord” might be more appropriate. You could write it a little more simply like this:

public static bool IsLongWord(string word)
{
    return word.Length > 3 && !Regex.IsMatch(word, "^[0-9]+$");
}