I have a lingering question. How does the practice of zazen relate to the development of compassion for our fellow sentient beings?

I believe I somewhat understand how the concept of 'oneness' (by which I mean dissolving the duality of 'I' and 'other') developed during zazen fosters a sense of compassion for the world as a whole. This type of compassion seems useful when I think of volunteering, giving dana to organizations that help the needy, and the like.

However, I think I have trouble breaking that apart into helpful nuggets of compassion that I can use in my day to day life in situations where I'm working with anger, frustration, and all those other fun defilements. Maybe it is the attempt to break it apart that's causing me trouble. I feel like there's a key piece I'm missing that will connect zazen and compassion for me in my day to day life. Any insight from others is much appreciated. Please correct me where my understanding is misguided or incomplete...

- Al