Rails get unique country with cities - ruby-on-rails

Question

How can I list unique country followed by related cities? Following were my product table:
name country city
p1 US New York
p2 US Boston
p3 US Chicago
k1 UK London
k2 UK Liverpool
Controller:
#countries = Product.joins(:user).distinct.where("country is not null and country <> ''").where(:users => {:merchant_status => 1}).pluck(:country)
#cities = Product.joins(:user).distinct.where("city is not null and city <> ''").where(:users => {:merchant_status => 1}).pluck(:city)
#countries.map! {|country| country.split.map(&:capitalize).join(' ')}
#search_location_country = #countries
And in my View:
<ul id="color-dropdown-menu" class="dropdown-menu dropdown-menu-right" role="menu">
<% #search_location_country.each do |country| %>
<li class="input"><%= country %></li>
<% end %>
</ul>
How can I sort the end result for drop down like this:
US
- New York
- Boston
- Chicago
UK
- London
- Liverpool
Thanks!!
EDIT
To be display something like this:

Answer 1

Hey you can try this way using group it gives you all distinct records
#countries_cities = Product.joins(:user).where("country is not null and country <> ''").where("city is not null and city <> ''").where(:users => {:merchant_status => 1}).group(:country, :city).select("country,city").as_json
It will give you output like
[{:country => "US", :city => "New York"}..]
If you want to again group it by country then used like
cchs = #countries_cities.group_by{|cc| cc["country"]}
Convert above multidimensional array to hash using
#country_cities_hash = = Hash[*cchs]
In your view file as
<% #country_cities_hash.each do |country, cities| %>
<li class="input"><%= country %></li>
<% cities.each do |city| %>
<li class="input"><%= "#{city}(#{country})" %></li>
<% end %>
<% end %>

Answer 2

Not sure I do understand the question but... I guess you have a collection of Product, looking like this :
produts = [
<Product #name="p1", #country="US" #city="New York">,
<Product #name="p1", #country="US" #city="Boston">,
<Product #name="k2", #country="FR" #city="Paris">,
...
]
In that case, to index the city names by country :
#cities_by_coutry = products.inject({}) do |index, product|
index[product.country] ||= []
index[product.country] << product.city
index
end
Which result to :
{"US"=>["New York", "Boston"], "FR"=>["Paris"]}
Then you can iterate :
#cities_by_coutry.each do |country, cities|
cities.each do |city|
puts "City: #{city} is in country {country}"
end
end