Using SequenceEqual and then returning which elements don't match

Question

I have two List<string> and I am using the SequenceEqual method to determine if they match.

I now have a need to get a List<int>, string, IEnumerable, whatever of the indexes of the elements that have failed.

Is there an easy way?

Thanks

Answer 1

I think you want:

List<string> list1 = ...
List<string> list2 = ...

var differentIndices = list1.Zip(list2, (item1, item2) => item1 == item2)
                            .Select((match, index) => new { Match = match, Index = index })
                            .Where(a => !a.Match)
                            .Select(a => a.Index);

Note that if one of the lists is longer than the other, this will not consider the items beyond the length of the smaller list.

Answer 2

You can use LINQ:

var firstFiltered = firstList.Except(secondList);
var secondFiltered = secondList.Except(firstList);

var bothFiltered = firstFiltered.Concat(secondFiltered);

---

Note: I'm sure there is a more efficient way of doing this...

Answer 3

It sounds like you want the opposite of the "intersection". The intersection is the items that exist in both lists ... and you want the items that don't exist in both lists.
Here's a easy one-liner to do that:

var items = first.Union(second).Except(first.Intersect(second));

Example:

var first = new[]{"A","B","C","D"};
var second = new[]{"C","D","E","F"};

var items = first.Union(second).Except(first.Intersect(second));
// Result: "A","B", "E","F"