title: Subsetting on a tibble using "[]" gives "object not found" error
body: <p>The article on dplyr <a href="http://seananderson.ca/2014/09/13/dplyr-intro.html" rel="nofollow noreferrer">here</a> says "[]" (square brackets) can be used to subset filtered Tibbles like this:</p>
  
  <pre><code>filter(mammals, adult_body_mass_g &gt; 1e7)[ , 3]
  </code></pre>
  
  <p>But I am getting an "object not found" error. 
  Here is the replication of the error on a more known dataset "iris"</p>
  
  <pre><code>library(dplyr)
  iris %&gt;% filter(Sepal.Length&gt;6) [,c(1:3)]
  </code></pre>
  
  <blockquote>
    <p>Error in filter_(.data, .dots = lazyeval::lazy_dots(...)) : 
      object 'Sepal.Length' not found</p>
  </blockquote>
  
  <p>I also want to mention that I am deliberately not preferring to use the native subsetting in dplyr using <code>select()</code> as I need a vector output and not a data frame on a single column. Unfortunately, dplyr always forces a data frame output (for good reasons).</p>