title: ggplot and scale_x_continuous
body: <p>here a sample of data :</p>
  <pre><code>library(ggplot2)
  lbreaks=c(-800,-600,-400,-300,-200,-100,-75,-50,-25,0,25,50)
  ddf=data.frame(x=lbreaks,
  y=seq(1,length(lbreaks),1))
  </code></pre>
  <p>and the scatter plot corresponding
  <a href="https://i.stack.imgur.com/exZdD.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/exZdD.jpg" alt="enter image description here" /></a></p>
  <p>I would use a custom scale (log or something similar for positive and negative values) for x-axis values to generate the same scatterplot with the equally spaced interval of x values. I tried to use several function in <code>scale_x_continuous(trans = </code> without sucess.
  How could I do this ?
  Many thanks for your help,</p>