grouped_options_for_select

Returns a string of <option> tags, like options_for_select, but wraps them with <optgroup> tags.

Parameters:

• grouped_options - Accepts a nested array or hash of strings. The first value serves as the <optgroup> label while the second value must be an array of options. The second value can be a nested array of text-value pairs. See options_for_select for more info.

   Ex. ["North America",[["United States","US"],["Canada","CA"]]]
  

• selected_key - A value equal to the value attribute for one of the <option> tags, which will have the selected attribute set. Note: It is possible for this value to match multiple options as you might have the same option in multiple groups. Each will then get selected="selected".
• prompt - set to true or a prompt string. When the select element doesn’t have a value yet, this prepends an option with a generic prompt — "Please select" — or the given prompt string.

Sample usage (Array):

  grouped_options = [
   ['North America',
     [['United States','US'],'Canada']],
   ['Europe',
     ['Denmark','Germany','France']]
  ]
  grouped_options_for_select(grouped_options)

Sample usage (Hash):

  grouped_options = {
   'North America' => [['United States','US], 'Canada'],
   'Europe' => ['Denmark','Germany','France']
  }
  grouped_options_for_select(grouped_options)

Possible output:

  <optgroup label="Europe">
    <option value="Denmark">Denmark</option>
    <option value="Germany">Germany</option>
    <option value="France">France</option>
  </optgroup>
  <optgroup label="North America">
    <option value="US">United States</option>
    <option value="Canada">Canada</option>
  </optgroup>

Note: Only the <optgroup> and <option> tags are returned, so you still have to wrap the output in an appropriate <select> tag.