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I have two association lists, whose values are integers, sharing some but not all keys. For a small example, we might have

A=<|x->1, y->2, z->3|>;
B=<|y->-2, z->7, w->0|>;

I would like to "add" the two association lists, by adding values when they share a common key, but also I would like to drop any keys whose values are 0. Thus, for my example I would want

Add(A,B)=<|x->1, z->10|>;

I can think of some ways to accomplish these tasks, but they are somewhat slow. Any advice?


Edited to add: In practice the list A is much longer than the list B, and has no zero values. I'm going to replace A by Add(A,B) anyway, so it might be faster to update A using B in some way.

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One way to do it.

Merge[{A, B}, Total] // Select[# != 0 &]
(* <|x -> 1, z -> 10|> *)

If there are no 0 values in A you might want to remove the 0's from B before the Merge.

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Merge[{A, B}, Total] // DeleteCases@0

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