c# - how to get a SUM in Linq?

Question

I need to do the following, I have a List with a class which contains 2 integer id and count

Now I want to do the following linq query:

get the sum of the count for each id

but there can be items with the same id, so it should be summerized e.g.:

id=1, count=12
id=2, count=1
id=1, count=2

sould be:

id=1 -> sum 14
id=2 -> sum 1

how to do this?

Answer 1

Group the items by Id and then sum the Counts in each group:

var result = items.GroupBy(x => x.Id)
                  .Select(g => new { Id = g.Key, Sum = g.Sum(x => x.Count) });