Grouping fields

I would like to group the output by date, so that between "root node" and "item node" there is a "group node". In this case I would like to group by date, so that all items with the same date are wrapped in the same "group node" tag.

Is this possible?

<root node>
  <day date="2014-01-22">
    <item node>
      <field1></field1>
      <field2></field2>
    </item node>
    <item node>
      <field1></field1>
      <field2></field2>
    </item node>
  </day>
  <day date="2014-01-23">
    <item node>
      <field1></field1>
      <field2></field2>
    </item node>
    <item node>
      <field1></field1>
      <field2></field2>
    </item node>
  </day>
<root node>