title: How to convert a column of formulas to include the data frame prefix in R
body: <p>How would I convert a column of R formulas to include the data frame specification?  For example I have a column of hundreds of formulas, but they don't contain any data frame spec, such as:</p>
  
  <pre><code>365/(x/y)
  365/(x/(y + z))
  365/(x/ (y - z))
  c + d + e + f
  </code></pre>
  
  <p>and I would like to convert the whole column to look like:</p>
  
  <pre><code>365/(r$x/r$y)
  365/(r$x/(r$y + r$z))
  365/(r$x/ (r$y - r$z))
  r$c + r$d + r$e + r$f
  </code></pre>
  
  <p>so I basically want to add a prefix(r$) to each text group separated by operators.  is this possible to do in R?</p>