title: delete duplicated column dplyr
body: <p>This morning while doing some analysis with a data frame I got an error due to the presence of duplicated column names. I tried to find a solution using exclusively dplyr but I could not find anything that works. Here is an example to illustrate the problem. A dataframe with a duplicated column name.</p>
  
  <pre><code>x &lt;- data.frame(matrix(c(1, 2, 3),
                  c(2,2,1),nrow=2,ncol=3))
  colnames(x) &lt;- c("a", "a", "b")
  </code></pre>
  
  <p>When I try to drop the first column using the select command I get an error</p>
  
  <pre><code>x %&gt;%
    select(-1)%&gt;%filter(b&gt;1)
  
  Error: found duplicated column name: a
  </code></pre>
  
  <p>I can get rid of the column easily using traditional indexing and the using dplyr to filter by value</p>
  
  <pre><code>x&lt;-x[,-1]%&gt;%filter(b&gt;1)
  </code></pre>
  
  <p>Which produces the desired output</p>
  
  <pre><code>&gt; x
    a b
  1 2 3
  2 2 3
  </code></pre>
  
  <p>Any ideas on how to perform this using only dplyr grammar?</p>