title: Find lowest price each day in list of documents
body: <p>we store in elasticsearch  documents  with following fields</p>
  
  <p>a (keyword)
  b (keyword)
  c (keyword)
  date (date-time)
  p (long)</p>
  
  <p>how to find the lowest value p each <code>date</code> between 12/1/1920 and 12/31/1920 (pacific time zone)</p>