Thanks very much @issa! Wrapping things together was what was needed, and I just had no idea how to do that successfully! I did have to modify to keep the right data and make the choice filter kick in for the state level when doing the county level. Here’s what worked in the queries, callback for the county level:
(function() {
var seen = { };
return _.chain(context).filter(function(place) {
var keep = (seen[place.state] !== true);
seen[place.state] = true;
return keep; })
.map(function(place) {
place.name = place.state;
place.label = place.state;
place.data_value = place.name;
place.display = {text:place.label};
return place;
}).value();
})()
This successfully gave me a unique list of counties within the states I had selected on the previous level, even when there were repeated observations for counties in the csv of the multi-level list because they contained multiple cities.