title: Pandas drop duplicates where condition
body: <p>I would like to <code>df.drop_duplicates()</code> based off a subset, but also ignore if a column has a specific value. </p>
  
  <p>For example...</p>
  
  <pre><code>                 v1      v2     v3      
  ID                                                          
  148         8751704.0    G      dog   
  123         9082007.0    G      dog  
  123         9082007.0    G      dog 
  123         9082007.0    G      cat   
  </code></pre>
  
  <p>I would like to drop duplicate <code>[ID, v1]</code> but ignore if <code>v3</code> is equal to <code>cat</code> so something like this: </p>
  
  <p><code>full_df.drop_duplicates([ID, v1], inplace=True, conditional=exclude v3 = cat)</code></p>
  
  <p>Hope that makes sense </p>