title: Removing stop words with tidytext
body: <p>Using tidytext, I have this code:</p>
  
  <pre><code>data(stop_words)
  tidy_documents &lt;- tidy_documents %&gt;%
        anti_join(stop_words)
  </code></pre>
  
  <p>I want it to use the stop words built into the package to write a dataframe called tidy_documents into a dataframe of the same name, but with the words removed if they are in stop_words.</p>
  
  <p>I get this error:</p>
  
  <p>Error: No common variables. Please specify <code>by</code> param.
  Traceback:</p>
  
  <pre><code>1. tidy_documents %&gt;% anti_join(stop_words)
  2. withVisible(eval(quote(`_fseq`(`_lhs`)), env, env))
  3. eval(quote(`_fseq`(`_lhs`)), env, env)
  4. eval(expr, envir, enclos)
  5. `_fseq`(`_lhs`)
  6. freduce(value, `_function_list`)
  7. withVisible(function_list[[k]](value))
  8. function_list[[k]](value)
  9. anti_join(., stop_words)
  10. anti_join.tbl_df(., stop_words)
  11. common_by(by, x, y)
  12. stop("No common variables. Please specify `by` param.", call. = FALSE)
  </code></pre>