title: Change column value by row string value in R
body: <p>I'm having a problem with a set of data.
  I want to change the values of a column, only for certain values in the rows of data.
  My table has this structure:</p>
  
  <pre><code>  Var1   Var2
  1   A    High
  2   A    High
  3   A    High
  4   B    High
  5   B    High
  6   B    High
  7   C    High
  8   C    Low
  9   C    Low
  10  C    Low
  </code></pre>
  
  <p>Now, I want to change the "Var2" values to "Medium", only when Var 1 is C.
  Thank you for help! :)
  Alin.</p>