title: How to order a data frame by one descending and one ascending column?
body: <p>I have a data frame, which looks like that: </p>
  
  <pre><code>    P1  P2  P3  T1  T2  T3  I1  I2
  1   2   3   5   52  43  61  6   "b"
  2   6   4   3   72  NA  59  1   "a"
  3   1   5   6   55  48  60  6   "f"
  4   2   4   4   65  64  58  2   "b"
  </code></pre>
  
  <p>I want to sort it by I1 in descending order, and rows with the same value in I1 by I2 in ascending order, getting the rows in the order <code>1 3 4 2</code>. But the <code>order</code> function seems to only take one <code>decreasing</code> argument, which is then <code>TRUE</code> or <code>FALSE</code> for all ordering vectors at once. How do I get my sort correct?</p>