<p>Please refer to <a href="https://arxiv.org/pdf/1306.2597.pdf" rel="nofollow noreferrer">Introducing LETOR 4.0 Datasets
</a> on page 2: as explained in the article:</p>

<blockquote>
  <p>Blockquote Each row is a query-document pair. The first column is relevance label of this pair,
  the second column is query id, the following columns are features, and the end of
  the row is comment about the pair, including id of the document. The larger the
  relevance label, the more relevant the query-document pair</p>
</blockquote>

<p>I hope it helps</p>
Letor dataset format
<p>I just discovered the Letor dataset used for learning to rank problem. I'm wondering what are the last two columns "inc" and "prob" stands for in train/test/vali set? 
Thanks</p>