title: groupby and filter pandas
body: <p>df:</p>
  
  <pre><code>    make    country other_columns   sale
  honda   tokyo   data    1
  honda   hirosima    data    0
  toyota  tokyo   data    1
  toyota  hirosima    data    0
  suzuki  tokyo   data    0
  suzuki  hirosima    data    0
  ferrari tokyo   data    1
  ferrari hirosima    data    0
  nissan  tokyo   data    1
  nissan  hirosima    data    0
  </code></pre>
  
  <p>Condition:
  keep pairs that have 1,0</p>
  
  <p>desired output</p>
  
  <pre><code>make    country other_columns   sale
  honda   tokyo   data    1
  honda   hirosima    data    0
  toyota  tokyo   data    1
  toyota  hirosima    data    0
  ferrari tokyo   data    1
  ferrari hirosima    data    0
  nissan  tokyo   data    1
  nissan  hirosima    data    0
  </code></pre>
  
  <p>What i tried (which is obviously not working )</p>
  
  <pre><code>outdf = df.groupby('sale').filter(lambda x: x &gt; 0)
  </code></pre>
  
  <p>should i be grouping both the columns ('sale' and 'make')?</p>