title: multiple transform on df with plyr
body: <p>I have a df and I want to do multiple transform on it with plyr:</p>
  
  <pre><code>idplot / idtree / species /  condition / dbh_cm / h_m / hblc_m
  
  
  CalcG &lt;- function (df) transform(df, g_m2 = pi * (dbh_cm^2)/40000)
  
  CalcHD &lt;- function (df) transform(df, hd = h_m / dbh_cm)
  </code></pre>
  
  <p>...</p>
  
  <p>Can be done in one function?
  Many thanks.</p>