Remove duplicates while merging lists using Union in LINQ

Question

I am trying to merge two lists using list.Union in LinqPad but I can\'t get it to work and wanted to check my understanding is correct.

Giv

Answer 1

You can try something like that if not happy with default comparer (which is, in turn, utilizes GetHashCode method as @IlyaIvanov had mentioned):

// get all items that "other than in first list", so Where() and Any() are our filtering expressions
var delta = list2.Where(x2 => !list.Any(x1 => (x1.Id == x2.Id) && (x1.field1 == x2.field1)));

// now let merge two enumerables that have nothing "equal" between them
var merged = list.Union(delta).ToList();