Load a hash on grouped_collection_select rails form - ruby-on-rails

Question

currently, I have a hash like this:
#lg = {
"Latin East Group" => [
{:id => 2, :name => "HONGKONG"},
{:id => 3, :name => "NINGBO, ZHEJIANG"},
{:id => 4, :name => "SINGAPORE"},
{:id => 5, :name => "LARCHMONT, NY"},
{:id => 6, :name => "CHICAGO, IL"},
{:id => 7, :name => "HAIPHONG"},
{:id => 8, :name => "DANANG"},
{:id => 9, :name => "HANOI"},
{:id => 10, :name => "MARSEILLE"},
{:id => 11, :name => "LONDON"},
{:id => 12, :name => "EDINBURGH"},
{:id => 13, :name => "AMSTERDAM"},
{:id => 14, :name => "HOCHIMINH"},
{:id => 15, :name => "SHANGHAI"}
],
"Latin West Group" => [],
"Others" => [
{:id => 16, :name => "Brazil" },
{:id => 17, :name => "Mexico" },
{:id => 18, :name => "Columbia"}
]
}
Now, I am using select2 with my form, and I wanna create a dropdown menu from that hash instance variable. I want the keys of the hash will be the optgroups, and the option values are gonna be the name sin the hash like Singapore, Brazil... Therefore, I am wondering what is the correct syntax for it. Currently, this is my code:
_form_body.haml:
%div.col-md-8
= f.grouped_collection_select :origin_locations, #lg, #lg.keys, #lg.values, {:selected => f.options[:origin_locations]}, {class: 'form-control select2-multiple origin_locations', :multiple => true}
pricing_histories_controller.rb:
def load_location_groups
#lg = {}
location_groups = LocationGroup.all.includes(:locations).each { |group|
#lg[group.name]= group.locations.map{|l| {id: l.id,name: l.name}}
}
# location_groups.each_with_index do |location_group, index|
arr = Location.where("id NOT IN (SELECT DISTINCT(location_id) FROM location_group_assignments)").pluck(:id,:name)
#location_groups = {}
#lg["Others"] = arr.map{ |e| {id: e.first, name: e.last}}
end
I will get the error:
ActionView::Template::Error (["Latin East Group", "Latin West Group",
"Others"] is not a symbol nor a string)
So, I am wondering what I am doing wrong here. Any suggestions would be appreciated. Thanks and have a nice day.