title: How can I subset a data frame based on duplicates in the last column?
body: <p>I have a data frame in R that looks like this:</p>
  
  <pre><code>st  cd  ct   bg  bg2  pop
  1   1   al   5   5.4  99
  1   1   al   2   4.2  93
  1   1   al   6   3.9  93
  1   1   al   8   53.  45
  1   1   al   1   5.4  08
  </code></pre>
  
  <p>How can I subset it so that the data frame is split up into two data frames, that contain all values except ones that are repeated in the last column?  For example, the above data frame would be subset-ted into:</p>
  
  <pre><code>st  cd  ct   bg  bg2  pop
  1   1   al   5   5.4  99
  1   1   al   2   4.2  93
  1   1   al   8   53.  45
  1   1   al   1   5.4  08
  </code></pre>
  
  <p>and </p>
  
  <pre><code>st  cd  ct   bg  bg2  pop
  1   1   al   5   5.4  99
  1   1   al   6   3.9  93
  1   1   al   8   53.  45
  1   1   al   1   5.4  08
  </code></pre>
  
  <p>Since 93 is repeated twice in the last column, pop, it would be split up, with one row into one data frame, and one row into another?  Is there an easy way to do this?</p>
  
  <p>Thanks for all the help.</p>