title: Error: row_number() should only be called in a data context
body: <p>I have used this string of code in R for months and months.  Just now running it it came up with an error where I haven't before. Here is the code:
  dat &lt;- dat %&gt;%
  mutate(row = row_number())
  Here is the error:
  Error: row_number() should only be called in a data context
  The data frame &quot;dat&quot; is a normal data frame of 8 columns and 400,000 rows.</p>