title: groupby that contain more than one element
body: <p>I am trying to recover in a DataFrame the rows of the groups (by TYPE) that contain more than one element.</p>
  
  <pre><code>TYPE VALEUR
  M1   A
  M1   B
  M2   A
  </code></pre>
  
  <p>the result should be :</p>
  
  <pre><code>TYPE VALEUR
  M1   A
  M1   B
  </code></pre>
  
  <p>Thanks!</p>