title: Pandas: boxplot of one column based on another column
body: <p>Say I have a dataframe like the following:</p>
  
  <pre><code>my_dataframe:
  
     Age  Group
  0  31   A
  1  24   A
  2  25   A
  3  36   A
  4  50   NaN
  5  27   A
  6  49   A
  7  24   A
  8  63   A
  9  25   A
  10  65  A
  11  67  A
  12  59  A
  13 NaN  B
  14  30  B
  15  19  B
  16  57  B
  17  62  B
  18  30  B
  19  50  B
  20  42  B
  21  45  C
  22  59  C
  23  28  C
  24  37  C
  25  29  C
  </code></pre>
  
  <p>I would like to boxplot the age of each Group (A,B,C). <strong>Note</strong> that I have some <code>NaN</code> values in the dataframe. How can I do this in Pandas?</p>