title: How I can find out max and min value of each day from hourly data sets
body: <p>This is hourly data of 2 years and I required max and min of daily data, how can I find this? </p>
  
  <pre><code>                     value
  record ts                 
  2014-01-01 00:00:00   5.83
  2014-01-01 01:00:00   5.38
  2014-01-01 02:00:00   4.80
  2014-01-01 03:00:00   3.81
  2014-01-01 04:00:00   4.46
  2014-01-01 05:00:00   5.04
  2014-01-01 06:00:00   5.76
  2014-01-01 07:00:00   6.15
  2014-01-01 08:00:00   6.66
  2014-01-01 09:00:00   7.02
  2014-01-01 10:00:00   7.43
  2014-01-01 11:00:00   7.34
  2014-01-01 12:00:00   7.24
  2014-01-01 13:00:00   7.71
  2014-01-01 14:00:00   8.89
  2014-01-01 15:00:00  10.31
  </code></pre>