title: Adding a general abline in log-log ggplot2
body: <p>I am trying to add a line to separate part of data in ggplot2. Following this thread:
  <a href="https://stackoverflow.com/questions/20617261/adding-linear-model-abline-to-log-log-plot-in-ggplot">Adding linear model abline to log-log plot in ggplot</a></p>
  
  <p>I tried</p>
  
  <pre><code>d = data.frame(x = 100*rlnorm(100), y = 100*rlnorm(100))
  ggplot(d, aes(x, y)) + geom_point() + 
    geom_abline(intercept = 100, slope = -1, col='red') +
    scale_y_log10() + scale_x_log10()
  </code></pre>
  
  <p>but it did not plot the line. Note that the old plot approach got the line alright:</p>
  
  <pre><code>plot(d$x, d$y, log='xy')
  abline(a = 100, b=-1, col='red', untf=TRUE)
  </code></pre>