title: Assigning pch symbols in plot
body: <p>I have a plot of many omega values within which I want to highlight about 40 points among the many others. The plot argument I am using is:</p>
  
  <pre><code>plot( log( dog[ order( dog$gbm.dog ) , 8 ] ), 
       pch = ifelse( dog$refseq_mrna %in% dog_omegaplus$refseq_mrna, 2,
             ifelse( dog$refseq_mrna %in% dog_omegaminus$refseq_mrna, 12, "." ) ) )
  </code></pre>
  
  <p>I want to have one group of highlighted points to be triangles (<code>pch = 2</code>), the other group to be squares (<code>pch = 12</code>) and all other points dots ("."). The problem is that the plot this produces has digits where the <code>pch</code> symbols should be (specifically a "2" where there should be triangles and a "1" where there should be squares).</p>
  
  <p>How do I designate the symbols correctly? </p>