title: Pandas .dropna() on specify attribute
body: <p>I have this code to drop null values from column Type, specifically looking at Dog.</p>
  
  <pre><code>cd.loc[cd['Type'] == 'Dog'].dropna(subset = ['Killed'], inplace = True)
  </code></pre>
  
  <p>I would like to dropna when the ['Killed'] column associating with Type = Dog has NaN value.</p>
  
  <p>The code above generate this pandas error:</p>
  
  <pre><code> A value is trying to be set on a copy of a slice from a DataFrame
  </code></pre>
  
  <p>Is there another way where can I dropna on ['Killed'] when ['Type'] == 'Dog'?</p>
  
  <p>(This is my first post), sorry if I can't explain properly
  Cheers</p>