title: Extract a dplyr tbl column as a vector
body: <p>Is there a more succinct way to get one column of a dplyr tbl as a vector, from a tbl with database back-end (i.e. the data frame/table can't be subset directly)?</p>
  
  <pre><code>require(dplyr)
  db &lt;- src_sqlite(tempfile(), create = TRUE)
  iris2 &lt;- copy_to(db, iris)
  iris2$Species
  # NULL
  </code></pre>
  
  <p>That would have been too easy, so</p>
  
  <pre><code>collect(select(iris2, Species))[, 1]
  # [1] "setosa"     "setosa"     "setosa"     "setosa"  etc.
  </code></pre>
  
  <p>But it seems a bit clumsy.</p>