title: Observe property on an array of objects for any changes
body: <p>I am using <a href="http://aurelia.io">Aurelia</a> and I have an array of items bound to a grid and they have a selected property on them. I want to bind a button to be enabled when any one of the items is true. I can do a brute force approach where I have a getter that is filtering the list and returning the selected items, but that means that I would be doing dirty checking constantly in the app and I don't want to do that. I am hoping for a more efficient approach. Any ideas?</p>