How to do "nothing" in the else part of ternary operator

Question

I want to filter values of a list based on whether or not they are contained in some other list. If an element is in the list I will select it, else I want to skip it or basically do nothing.

Below is what I tried to do. How can I achieve this?

List<string> sheetNames = new List<string>() {"1","10"};
List<string> projects= new List<string>() {"1","2","3","4","5","6","7"};

IEnumerable<string> result =  
    sheetNames.Select(x => projects.Contains(x) 
                               ? x 
                               : /*Want to do nothing here */);

Answer 1

You can use Enumerable.Intersect method to get the common values from the two lists.

IEnumerable<string> commonValues = projects.Intersect(sheetNames);

Answer 2

List<string> sheetNames = new List<string>() {"1","10"};
List<string> projects= new List<string>() {"1","2","3","4","5","6","7"};

IEnumerable<string> result = sheetNames.Where(x => projects.Contains(x));