I was asked to help a fellow Mendix developer with some workflow issues and something stood out: There were a LOT of nested loops. Though preached (commanded?) by computer science professors as bad practice for very good reasons, we all know in the 'real world' outside of the walls of academia that sometimes you require the kind of result that can only be achieved by comparing multiple lists as they relate to each other. This creates a massive amount of overhead on a single-threaded application and can render an application useless if those lists are sizable. Sure, domain modeling is often to blame, but tools like what Mendix provides are supposed to make it easier for non-developers to do this kind of thing. There is a better way, and Mendix provides a set of actions to help you deal with these in a more efficient way: List Operations.