title: Find row name in R
body: <p>I wonder how I can extract row name from row number?</p>
  
  <pre><code>x &lt;- data.frame( A = 1:10, B = 21:30 )
  rownames( x ) &lt;- sample( LETTERS, 10 )
  &gt; x
     A  B
  J  1 21
  A  2 22
  I  3 23
  G  4 24
  H  5 25
  B  6 26
  P  7 27
  Z  8 28
  O  9 29
  R  10 30
  &gt; x[ "H",]
    A  B 
  H 5 25
  </code></pre>
  
  <p>I want to find what is the row name of specific row? for example row name of row=3</p>
  
  <p>also which rowname contains the value 30?</p>
  
  <p>thanks</p>