title: How to get summary statistics by group
body: <p>I'm trying to get multiple summary statistics in R/S-PLUS grouped by categorical column in one shot. I found couple of functions, but all of them do one statistic per call, like <code>aggregate()</code>.</p>
  <pre><code>data &lt;- c(62, 60, 63, 59, 63, 67, 71, 64, 65, 66, 68, 66, 
            71, 67, 68, 68, 56, 62, 60, 61, 63, 64, 63, 59)
  grp &lt;- factor(rep(LETTERS[1:4], c(4,6,6,8)))
  df &lt;- data.frame(group=grp, dt=data)
  mg &lt;- aggregate(df$dt, by=df$group, FUN=mean)    
  mg &lt;- aggregate(df$dt, by=df$group, FUN=sum)    
  </code></pre>
  <p>What I'm looking for is to get multiple statistics for the same group like mean, min, max, std, ...etc in one call, is that doable?</p>