option_groups_from_collection_for_select

Returns a string of option tags, like options_from_collection_for_select, but surrounds them with <optgroup> tags.

An array of group objects are passed. Each group should return an array of options when calling group_method Each group should return its name when calling group_label_method.

html_option_groups_from_collection(@continents, "countries", "continent_name", "country_id", "country_name", @selected_country.id)

Could become:

 <optgroup label="Africa">
  <select>Egypt</select>
  <select>Rwanda</select>
  ...
 </optgroup>
 <optgroup label="Asia">
  <select>China</select>
  <select>India</select>
  <select>Japan</select>
  ...
 </optgroup>

with objects of the following classes: class Continent

  def initialize(p_name, p_countries) @continent_name = p_name; @countries = p_countries; end
  def continent_name() @continent_name; end
  def countries() @countries; end

end class Country

  def initialize(id, name) @id = id; @name = name end
  def country_id() @id; end
  def country_name() @name; end

end

NOTE: Only the option tags are returned, you have to wrap this call in a regular HTML select tag.