Trying to combine Users into the same marker using gmaps4rails - ruby-on-rails

Question

I can't figure out how to combine users into the same markers in gmaps4rails. I feel like I'm somewhat close, but can't exactly figure out what I'm doing wrong between using the gmaps4rails helper, converting to JSON, and rendering by partial.
def map
distinct_locations = User.where("location IS NOT NULL").select("DISTINCT(LOCATION)").map(&:location)
#markers = []
distinct_locations.each do |city|
temp_marker = User.where(:location => city).first.to_gmaps4rails
city_users = User.where(:location => city)
render_to_string(:partial => "/users/map_marker_info", :locals => { :users => city_users})
#markers << temp_marker
end
#markers
end
As you can see, in my controller, I first get an array of distinct_locations, which is just an array of city names (like "New York, New York").
Then I create the #markers to hold the JSON I'll eventually return.
For each unique city that I found, I'm TRYING to first create a marker using the to_gmaps4rails helper using the first User I find in that city. Then I'm trying to find all the other users in the city (via city_users = User.where(:location => city).
I'm then trying to render my partial using this collection of Users in the same city with something like this for now (but eventually will pull different attributes from Users):
#_map_marker_info.html.haml
.map_info_window
%h4
=users.first.location
%p
=users.count
Finally, I add the marker to #markers after each city is processed.
Eventually, I return #markers as a JSON that then becomes a beautiful map thanks to the awesome gmaps4rails gem.
I'm sure I'm doing a lot of things wrong (and probably many things inefficiently)...but can someone help me just to get it working?

Answer 1

Well, just one of those moments when things crystallize after you post a question. Anyways, here's what I have and it works. (Though still open to people giving more efficient answers). This "custom marker" is very very similar to the official documentation:
https://github.com/apneadiving/Google-Maps-for-Rails/wiki/Controller
def map
#markers = User.select("DISTINCT ON (location) *").where("location IS NOT NULL").all.to_gmaps4rails do |user, marker|
city_users = User.where(:location => user.location)
marker.infowindow render_to_string(:partial => "/users/map_marker_info", :locals => { :users => city_users })
end
end
Basically, select Users based on distinct locations (you really only need the latitude and longitude columns for the to_gmaps4rails helper to work. Also I removed the nil values for people who don't have locations.
Then for each "location", essentially, create the marker, but for the locals, pass in all the Users with the same location. That's what city_users is for -- all the users in the same city.
And so now I can do something like this in my partial:
.map_info_window
%h4
=users.count
in
=users.first.location
-users.each do |user|
=link_to user.full_name, user