Set Operators

Using .Select() method returns a duplicate items. We use .Distinct() to differentiate with others.

birds.Select(b => b.Color);
// return "Red", "Black", "Red", ..

birds.Select(b => b.Color).Distinct();
// return "Red", "Black", ..

We could find items that are not in the collection. Like we want to find colors in one collection differ than bird colors.

var colors = new List<string> {"Pink", "Blue", "Black"};
colors.Except(birds.Select(b => b.Color).Distinct());
// return "Pink", "Blue"

Next is Union() operator. It takes both items in 2 collections and remove the duplicates.

colors.Union(birds.Select(b => b.Color));
// return "Pink", "Blue", "Black", "Red", "White", "Black"

Next is Intersect() operator. It only returns items that are exist in both collection.

colors.Intersect(birds.Select(b => b.Color).Distinct());
// return "Black"