Question

If I have a dictionary containing 2 or more lists, how can I quickly find shared items between these lists and add these shared items to a list external to the dictionary?

For example:

list1:

• eng;English
• lir;Liberian English

list2:

• eng;English
• bav;Vengo

list3:

• lat;Latin

extList:

• eng;English

This shared item is then removed from the lists inside the dictionary.
I have added list3 to show that a superfluous item may be ignored, and that I have specified 2 or more lists.

Answer 1

Suppose we have a list of lists (or a dictionary, which would add a Key):

List<List<string>> lists = new List<List<string>>()
{
    new List<string> {"Hello", "World", "7"},
    new List<string> {"Hello", "7", "Person"},
    new List<string> {"7", "7", "Hello"}
};

You can find items that are present in all lists:

List<string> extList = lists.Cast<IEnumerable<string>>()
                            .Aggregate((a, b) => a.Intersect(b)).ToList();

If you want to get strings that are common to just a few lists, you can use:

var counts = from str in lists.SelectMany(list => list)
             group str by str into g
             where g.Count() > 1
             select new { Value = g.Key, Count = g.Count() };

You can drop the last line if you don’t care how many times each word appears. Note that this will not tell you in which list the word is.