I've been thinking about this a lot lately and have made a few observations, but the thing that gets me is the exact relationship between the two. As I see it now, anger is a reaction to sadness in the majority, if not all cases. I believe that things trigger sad moods in us, anger arises as a technique to push away the sadness, and we use our anger to "touch" that sadness thereby deflating the anger, either by exposing sadness in someone else and reflecting it, or by needling our own feelings. So, my hypothesis is that anger is a way to distance the subject from depression/sadness.
The prime example is with abusive relationships. Guys gets abandonment anxiety. Abandonment depression (sadness) is looming, so he feels anger inside. The anger is generalized, but finds targets to project on. He could be angry at his dog, his kids, or his wife. The wife is the prime target being the source of the anger. He uses the anger to create sadness in his wife, reflects on that sadness (via mirror neurons) and touches his own sadness. The anger dissipates, since the depression and sadness has been reached and the anger no longer serves a purpose. He can then function alongside the depression instead of trying to avoid it, and is free to be himself without the worry and anxiety, and strengthen his relationship (honeymooning) until the next episode. Thoughts? Additions?