title: dplyr filtering with the %in% operator for two dataframes
body: <p>I have two dataframes.</p>
  
  <p>The first is my main pool, and the second is a "list" of names that I want to filter on.</p>
  
  <p>main:</p>
  
  <pre><code>aaa   bbb   ccc
  dog   1     2
  cat   2     4
  dog   1     2 
  dog   1     2  
  cat   3     2 
  snake 1     5
  snake 3     2
  </code></pre>
  
  <p>list1 (currently in a dataframe)</p>
  
  <pre><code>aaa
  dog
  cat
  </code></pre>
  
  <p>I want to use dplyr::filter and the %in% operator to subset the main pool:</p>
  
  <pre><code>sub &lt;- main %&gt;% filter(aaa %in% list1)
  </code></pre>
  
  <p>I thought the above would work, but it's creating a 0 row dataframe. </p>