title: connect points in ggplot based on specific column values
body: <p>I have the following data set called <code>t</code>:</p>
  
  <pre><code>n &lt;- 12
  t &lt;- data.frame(
    V1    = runif(n, 0.12, 0.35),
    V2    = runif(n, 0.25, 0.39),
    group = gl(3, 4, labels = c("a1", "a2", "a3")),
    x     = seq_len(n),
    color = rep(rep.int(c("R", "G"), 2), c(3, 4, 3, 2))
  )
  </code></pre>
  
  <p>I created the following plot from this data.</p>
  
  <pre><code>p &lt;- ggplot(t, aes(x, colour = color)) +  
    geom_point(aes(y = V1, size = 10)) + 
    geom_point(aes(y = V2, size = 10))
  </code></pre>
  
  <p>What I want to do now is to connect the points depending on the group column (e.g, points of group <code>a1</code> will be connected with a blue line, points of group <code>a2</code> will be connected in a yellow line, ...) and i want the line to be different depending on <code>V1</code> and <code>V2</code> (dashed line for <code>V1</code> and normal line for <code>V2</code>).</p>
  
  <p>How this can be done?</p>