To get the number unique values from a list you can create a Java set, which does not allow duplicate values

createObject("java", "java.util.HashSet").init(listToArray(valueList(eventsQuery.event_id))).size();

The init values requires a list, so if you already have a list, you can just pass that in to return a Java set object. You will need to convert the set back to a list to make it easy to work with in ColdFusion although you could iterate over it if you’d like. Here’s the easiest version.

listWithDupes = [1,2,3,1,3];
noDupes = createObject("java", "java.util.HashSet").init(listWithDupes);
noDupesArray = createObject("java", "java.util.ArrayList").init(noDupes);
writeDump(noDupesArray); //returns 1,2,3