title: How to groupby and average data greater than 0?
body: <p>I have a huge dataframe containing sensor data every 5 minutes.
  I added in a week number column. </p>
  
  <p>I want to sum up the sunlight sensor column by week, but want to average the temperature column (<code>if temp &gt; 0</code>). </p>
  
  <pre><code>ClimateDF.groupby('week').agg({'sunlight': 'sum', 'Temp': 'mean'})
  </code></pre>
  
  <p>This works, but how would I add in conditions? For example only average the temp <code>if temp &gt; 0</code> etc?</p>