title: summarise() - calculating percentages and counts of factor
body: <p>I'm trying to use summarise() from the plyr-packge to calculate percentages of occurences of each level in a factor. EDIT: The Puromycin data is in the base R installation</p>
  
  <p><strong>My data look like this:</strong></p>
  
  <pre><code>library(plyr)
  data.p &lt;- as.data.frame(Puromycin[,3])
  names(data.p) &lt;- "Treat.group" 
  </code></pre>
  
  <p><strong>I've done this:</strong></p>
  
  <pre><code>    summarise(  data.p, "Frequencies"= count(data.p), 
  "Percent" = count(data.p)/ sum(count(data.p)[2] ))
  </code></pre>
  
  <p><strong>And got this:</strong></p>
  
  <pre><code>  Frequencies.Treat.group Frequencies.freq Percent.Treat.group Percent.freq
  1                 treated               12                  NA    0.5217391
  2               untreated               11                  NA    0.4782609 
  </code></pre>
  
  <p>But I don't want the 3. column to be generated. It is unnecessary, and only shows NA.</p>
  
  <p><strong>How do I write the code so I don't get that NA column?</strong></p>
  
  <p>Any pointers are appreciated :)</p>