title: Sum of column values on individual month
body: <p>I have a dataframe like this:</p>
  
  <pre><code>Timestamp   Consumption
  4/1/2017 20:00  257
  4/1/2017 21:00  262
  4/1/2017 22:00  256
  4/1/2017 23:00  256
  4/2/2017 0:00   263
  4/2/2017 1:00   256
  4/2/2017 2:00   265
  4/2/2017 3:00   259
  4/2/2017 4:00   256
  4/2/2017 5:00   260
  4/2/2017 6:00   265
  4/2/2017 7:00   265
  </code></pre>
  
  <p>I want to do the sum of consumption column of individual months and put it in a list. Like :</p>
  
  <p>[1031,2089]</p>
  
  <p>And to do the sum according to time and irrespective of date. Like 23:00 hrs to 06:00 hrs:</p>
  
  <p>[2080]</p>
  
  <p>How can I achieve this? PLease Help. </p>