title: Remove level and all of its rows from pandas dataframe if one row meets condition
body: <p>Below is a pandas dataframe that I would like to filter. I would like to remove the year and all of its rows when the temp for at least one row (i.e., <code>visit</code>) in that year is &lt; 37. I am able to remove the specific row in 2014 where the temp is 36; however, I do not know how to make the entire year go away. </p>
  
  <pre><code>index = pd.MultiIndex.from_product([[2013, 2014], [1, 2]], names=['yr', 
                                                                    'visit'])
  columns = pd.MultiIndex.from_product(['hr', 'temp'], names=['metric'])
  data = pd.DataFrame([[96, 38], [98, 38], [85, 36], [84, 43]], index=index, 
                      columns=columns)
  data
  
          metric  hr      temp    
  yr      visit                       
  2013    1       96      38  
          2       98      38  
  2014    1       85      36  
          2       84      43  
  </code></pre>
  
  <p>Desired Output:</p>
  
  <pre><code>        metric  hr      temp    
  yr      visit                       
  2013    1       96      38  
          2       98      38  
  </code></pre>