title: new column with max difference in R
body: <p>I have a dataframe like:</p>
  
  <pre><code>A   1 2 3 4
  B   4 5 6 9
  C   2 3 4 5 
  </code></pre>
  
  <p>and I want to calculate the maximum difference for each row, and put it in new column:</p>
  
  <pre><code>A   1 2 3 4  3 (4-1)
  B   4 5 6 9  3  (9-6)
  C   1 3 4 5  4  (5-1)
  </code></pre>
  
  <p>Any ideas??</p>
  
  <p>Thank you!!!</p>