title: Calculating averages of time series data using pandas dataframe
body: <p>I have stumbled upon this thread:</p>
  
  <p><a href="https://stackoverflow.com/questions/29762546/monthly-averages-using-daily-data-using-python-pandas">Monthly Averages Using Daily Data Using Python Pandas</a></p>
  
  <p>which has answered most of my question. The remaining part is, how can I line up the results with the original data accordingly, like this:</p>
  
  <pre><code>1979    1   1   3
  1979    1   2   3
  1979    1   3   3
  1979    1   4   3
  1979    1   5   3
  1979    1   6   3
  1979    1   7   4
  1979    1   8   5
  1979    1   9   7
  1979    1   10  8
  1979    1   11  16
  1979    1   12  16
  1979    1   13  16
  1979    1   14  18
  1979    1   15  18
  1979    1   16  18
  1979    1   17  18
  1979    1   18  20
  1979    1   19  20
  1979    1   20  20
  1979    1   21  20
  1979    1   22  20
  1979    1   23  18
  1979    1   24  18
  1979    1   25  18
  1979    1   26  18
  1979    1   27  18
  1979    1   28  18
  1979    1   29  18
  1979    1   30  18
  1979    1   31  19  13.709677
  1979    2   1   19
  1979    2   2   19
  1979    2   3   19
  1979    2   4   19
  1979    2   5   19
  1979    2   6   22
  1979    2   7   24
  1979    2   8   27
  1979    2   9   29
  1979    2   10  32
  1979    2   11  32
  1979    2   12  32
  1979    2   13  32
  1979    2   14  33
  1979    2   15  33
  1979    2   16  33
  1979    2   17  34
  1979    2   18  36
  1979    2   19  36
  1979    2   20  36
  1979    2   21  36
  1979    2   22  36
  1979    2   23  36
  1979    2   24  31
  1979    2   25  29
  1979    2   26  27
  1979    2   27  27
  1979    2   28  27  29.107143
  </code></pre>
  
  <p>Thanks in advance</p>