Measuring replaced products/item

[#1]

I like to measure new products like this:

1) I select Appel in my filter

2) Now I like look at the IDs who has bought appel in 2015 but not i 2014 (In this case it's just Idkey = 4). Then I to show in my graph which items did idkey 4 bought in 2014 and how many (In this case it will be Lemon = 11). In other words I like to show which items has apple replaced and how many.

How do I create an expression to do the trick ?