title: Python Pandas check if a value occurs more then once in the same day
body: <p>I have a Pandas dataframe as below. What I am trying to do is check if a station has variable <code>yyy</code> and any other variable on the same day (as in the case of <code>station1</code>). If this is true I need to delete the whole row containing <code>yyy</code>. </p>
  
  <p>Currently I am doing this using <code>iterrows()</code> and looping to search the days in which this variable appears, changing the variable to something like "delete me", building a new dataframe from this (because <a href="https://stackoverflow.com/questions/15972264/why-doesnt-this-function-take-after-i-iterrows-over-a-pandas-dataframe">pandas doesn't support replacing in place</a>) and filtering the new dataframe to get rid of the unwanted rows. This works now because my dataframes are small, but is not likely to scale.</p>
  
  <p><strong>Question:</strong> This seems like a very "non-Pandas" way to do this, is there some other method of deleting out the unwanted variables?</p>
  
  <pre><code>                dateuse         station         variable1
  0   2012-08-12 00:00:00        station1               xxx
  1   2012-08-12 00:00:00        station1               yyy
  2   2012-08-23 00:00:00        station2               aaa
  3   2012-08-23 00:00:00        station3               bbb
  4   2012-08-25 00:00:00        station4               ccc
  5   2012-08-25 00:00:00        station4               ccc
  6   2012-08-25 00:00:00        station4               ccc
  </code></pre>