title: ggplot specific thick line
body: <p>How would one be able to plot one line thicker than the other. I tried using the <code>geom_line(size=X)</code> but then this increases the thickness of both lines. Let say I would like to increase the thickness of the first column, how would one be able to approach this?</p>
  
  <pre><code>a &lt;- (cbind(rnorm(100),rnorm(100)))  #nav[,1:10]
  sa &lt;- stack(as.data.frame(a))
  sa$x &lt;- rep(seq_len(nrow(a)), ncol(a))
  require("ggplot2") 
  p&lt;-qplot(x, values, data = sa, group = ind, colour = ind, geom = "line")
  p + theme(legend.position = "none")+ylab("Millions")+xlab("Age")+
  geom_line( size = 1.5)
  </code></pre>