title: Pandas groupby take counts greater than 1
body: <p>This must be a simple question, but, however, it is bugging my head for a while.</p>
  
  <p>For a dataframe below:</p>
  
  <pre><code>df = pd.DataFrame({'c0': ['a','b','a'],'c1': ['a','bb','a'],'c2':[10,20,30]})
    c0  c1  c2
  0  a   a  10
  1  b  bb  20
  2  a   a  30
  </code></pre>
  
  <p>How to get output where count > 1?</p>
  
  <p>I have tried:</p>
  
  <pre><code>df.groupby(['c0','c1'])['c2'].count()
  c0  c1
  a   a     2
  b   bb    1
  </code></pre>
  
  <p>Required is:</p>
  
  <pre><code>c0  c1
  a   a     2
  </code></pre>
  
  <p>I am looking other than</p>
  
  <pre><code>x = df.groupby(['c0','c1'])['c2'].count()
  x[x&gt;1]
  </code></pre>
  
  <p>i.e. a one-liner answer.</p>