Most efficient way to compare two lists and delete the same

Question

I want to compare two lists and get the valid words into a new list.

var words = new List();
var badWords = new List();

//this i         


        

Answer 1

Use Enumerable.Except:

List cleanList = words.Except(badWords).ToList();

This is efficient because Except uses a set based approach.

An even more efficient approach is to avoid that "bad" words are added to the first list at all. For example by using a HashSet with a case-insensitive comparer:

var badWords = new HashSet(StringComparer.InvariantCultureIgnoreCase){ "Idiot", "Retarded", "Twat", "Fool", "Moron" };

string word = "idiot";
if (!badWords.Contains(word))
    words.Add(word);