title: Add labels on lattice xyplot
body: <p>I have created a xyplot with lattice</p>
  
  <pre><code>library(lattice)
  X1=c(5, -2, 1, -3)
  X2=X1^2
  names=paste("dot", 1:4, sep="")
  xyplot(X2~X1, data=data.frame(X1, X2), pch=20, cex=1:4)
  </code></pre>
  
  <p>Now I want to add a label (text) for each dot. The info is in   </p>
  
  <pre><code>names=paste("dot", 1:4, sep="")
  </code></pre>
  
  <p>I have tried with no success the following</p>
  
  <pre><code>panel.text(x=X2, y=X1, names)
  </code></pre>
  
  <p>or, using directlabels</p>
  
  <pre><code>library(directlabels)
  p=xyplot(X2~X1,data=data.frame(X1, X2), pch=20, group=names, cex=1:4)
  direct.label(p,smart.grid,FALSE)
  </code></pre>
  
  <p>but I don't like it much because I had to split into groups using <code>group=names</code>, basically each dot is in a different group? Is there another way to do it?</p>