title: Error selecting a column after grouping the dataframe using group_by from dplyr 0.3.02
body: <p>I cannot select the second column after grouping the data.frame </p>
  
  <pre><code>d &lt;- data.frame(x = 1:10, y = runif(1))
  d[,2] # selects the second column
  d &lt;- group_by(d, x)
  d[,2] # produces the error: index out of bounds
  </code></pre>