title: Conditional formatting table with R
body: <p>I have a table:</p>
  
  <pre><code>Time Class  Type Value1 Value2
  2005  A      KS    5      6
  2005  B      KS    3      3
  2005  C      CS    6      6
  2006  A      CS    5      3
  2006  A      KS    9      2
  2006  B      KS    6      9
  2006  C      KS   39      6
  2007  C      CS   10      20
  2007  A      KS   26      23
  </code></pre>
  
  <p>I need to create new data set which contains only rows with the same "Class" and "Type" for each year. For example, for years 2005 and 2006 there are only two rows with the same (common) "Class" and "Type".</p>