gistfile1.rb

existing_invitee_user_ids = []
user_ids[:user_id].each_pair{|key, value|
  if value.to_i == 1
    existing_invitee_user_ids << key.to_i
  end
end
existing_invitee_user_ids.compact!
existing_invitee_user_ids.uniq!
existing_invitee_user_ids

-------

user_ids[:user_id].select{|k, v| v == "1"}.transpose.first.map{|id| id.to_i}