title: Monthly Averages Using Daily Data Using Python Pandas
body: <p>I have a text file with four columns: year, month, day and snow depth. This is daily data for a 30-year period, 1979-2009.</p>
  <p>I would like to calculate 360 (30yrs X 12 months) individual monthly averages using pandas (i.e. isolating all the values for Jan-1979, Feb-1979,... Dec-2009 and averaging each). Can anyone help me out with some example code?</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
  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
  </code></pre>