title: Select first 4 rows of a data.frame in R
body: <p>How can I select the first 4 rows of a <code>data.frame</code>:</p>
  
  <pre><code>              Weight Response
  1   Control     59      0.0
  2 Treatment     90      0.8
  3 Treatment     47      0.1
  4 Treamment    106      0.1
  5   Control     85      0.7
  6 Treatment     73      0.6
  7   Control     61      0.2
  </code></pre>