title: Finding ALL duplicate rows, including "elements with smaller subscripts"
body: <p>R's <code>duplicated</code> returns a vector showing whether each element of a vector or data frame is a duplicate of an element with a smaller subscript. So if rows 3, 4, and 5 of a 5-row data frame are the same, <code>duplicated</code> will give me the vector </p>
  
  <pre><code>FALSE, FALSE, FALSE, TRUE, TRUE
  </code></pre>
  
  <p>But in this case I actually want to get </p>
  
  <pre><code>FALSE, FALSE, TRUE, TRUE, TRUE
  </code></pre>
  
  <p>that is, I want to know whether a row is duplicated by a row with a <strong>larger</strong> subscript too.</p>