title: Limit number of lines read by d3.csv or d3.text
body: <p>When users of a web app upload a CSV, I want to display on screen a sample of the uploaded data. They could upload 2 to 20 million rows, so I want to limit the number being read by d3 (for speed) and displayed (for style) to, let's say, 100 rows.</p>
  
  <p>Is this possible? </p>
  
  <p>The <a href="https://github.com/d3/d3-request/blob/master/README.md#csv" rel="nofollow noreferrer">documentation</a> didn't make the answer apparent to me. I see that it says </p>
  
  <blockquote>
    <p>An optional row conversion function may be specified to map and filter
    row objects to a more-specific representation;</p>
  </blockquote>
  
  <p>But I don't really understand these row conversion functions or other filters and if they can only be applied after the file is read, or if they can be used to limit the rows being read.</p>