title: How to implement learning to rank using lightgbm?
body: <p>I'm trying to set up learning to rank with <code>lightgbm</code>, I have the following dataset with the interactions of the users based on the query:</p>
  <pre><code>df = pd.DataFrame({'QueryID': [1, 1, 1, 2, 2, 2], 
                     'ItemID': [1, 2, 3, 1, 2, 3], 
                     'Position': [1, 2 , 3, 1, 2, 3], 
                     'Interaction': ['CLICK', 'VIEW', 'BOOK', 'BOOK', 'CLICK', 'VIEW']})
  </code></pre>
  <p>The question is to properly set up the dataset for training? The docs mention using <code>Dataset.set_group()</code> but it's not very clear how.</p>