Active admin form customization

In my active admin form I'm retrieving multiple users with email, name, mobile attribute. I want to display this in table format and email, name, mobile as indexes.
Any help would be appreciated.../?

     f.input :user_ids, :label => "Users", 
  :multiple => true,  collection: @user.collect{|u| [[u.email, u.name, u.mobile].to_s.gsub('"',""), u.id]}, 
  :required => true, :input_html => { :class => "users_checkboxes", :size => 20