title: Create dummy variable in R excluding certain cases as NA
body: <p>I have data that looks like this:</p>
  
  <pre><code>V1 V2
  A  0
  B  1
  C  2
  D  3
  E  4
  F  5
  G  9
  </code></pre>
  
  <p>I want to create a dummy variable in <code>R</code> where <code>0 = {1}</code>,  <code>1 = {2,3,4}</code> and <code>NA = {0,5,9}</code></p>
  
  <p>Should be simple - can anyone help?</p>