dplyr mutate/transmute: drop only the columns used in the formula : <p>Suppose my data frame has columns A, B, C, D, E.</p>

<p>I want to produce a data frame with columns A, B, C, X, where X = D * E.</p>

<p>Obviously I can use <code>%&gt;% mutate(X = D * E) %&gt;% select (-D, -E)</code>, but for more elaborate situations, is there a way to do it in a single command?  Like <code>transmute()</code>, but only discarding the columns that were mentioned.</p>

<p>Silly, but I keep wishing for this bit of conciseness.</p>
