title: remove repeat values between two columns
body: <p>I have two columns (v1 and v2) such as:</p>
  <pre><code>v1 &lt;- c(0,0,1,0,1,0,0,0,1) v2 &lt;- c(1,1,1,0,1,1,1,0,1)
  </code></pre>
  <p>I want to create a new column (V3). The new column is exactly the same as v2, except that if there is a 1 in v1 that matches a 1 in v2, then that value changes to zero. Thus the desired solution looks like this:</p>
  <pre><code>v1 &lt;- c(0,0,1,0,1,0,0,0,1) 
  v2 &lt;- c(1,1,1,0,1,1,1,0,1) 
  v3 &lt;- c(1,1,0,0,0,1,1,0,0)
  </code></pre>