title: Matching based on multiple columns in dataframes
body: <pre><code>file1
     ID Length Breadth height qty1
  1 201   2500    1250   7.85 200
  2 201      0      10   5.85 245
  3 202      0       0   7.85 245
  
  file2
     ID Length Breadth height qty2
  1 201    250      12   7.85 200
  2 201      0      10   5.85 250
  3 202      0      12   8.00 200
  </code></pre>
  
  <p>I want all the rows where ID ,length , breadth &amp; height matches</p>
  
  <pre><code>match1= stock[(req$ID == stock$ID) &amp; (req$Length==stock$Length) &amp;
                 (req$Breadth==stock$Breadth) &amp; (req$height==stock$height),]
  match1
  
  ID Length Breadth height    qty1    qty2
  201  0        10    5.85    245     250
  </code></pre>