title: breaks without scale_y_continuous() in ggplot2
body: <p>I was searching for a method to set breaks in a plot without using the scale_y_...(breaks=c(x1,x2)) function. The problem is the following: I want some boxplots.</p>
  
  <pre><code>    require(ggplot2)
      a &lt;- rnorm(10, 0, 5)
      a &lt;- as.data.frame(a); colnames(a) &lt;- "test"
  
      ### original boxplot
      ggplot(data=a, mapping=aes(y=test, x=rep(1,10))) +
        geom_boxplot()
  
      ### scale_y_continous() cuts of my data points and changes the boxplot!
      ggplot(data=a, mapping=aes(y=test, x=rep(1,10))) +
        geom_boxplot() +
        scale_y_continuous(limits=c(-1,1), breaks=c(-1,0,1))
  
      ### I am therefore using coord_cartesian() but I am missing a breaks() function
      ggplot(data=a, mapping=aes(y=test, x=rep(1,10))) +
        geom_boxplot() +
        coord_cartesian(ylim = c(-1,1)) # +
      # breaks(c(-1,0,1))   # something like this
  </code></pre>
  
  <p>Thank you for your help!</p>