title: Is there a way of manipulating ggplot scale breaks and labels?
body: <p><code>ggplot</code> generally does a good job of creating sensible breaks and labels in scales.</p>
  
  <p>However, I find that in plot with many facets and perhaps a <code>formatter=</code> statement, the labels tend to get too "dense" and overprint, for example in this picture:</p>
  
  <pre><code>df &lt;- data.frame(
          fac=rep(LETTERS[1:10], 100),
          x=rnorm(1000)
  )
  
  ggplot(df, aes(x=x)) + 
    geom_bar(binwidth=0.5) + 
    facet_grid(~fac) + 
    scale_x_continuous(formatter="percent")
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/ThFOk.png" alt="enter image description here"></p>
  
  <p>I know that I can specify the breaks and labels of scales explicitly, by providing <code>breaks=</code> and <code>scale=</code> arguments to <code>scale_x_continuous</code>.</p>
  
  <p>However, I am processing survey data with many questions and a dozen crossbreaks, so need to find a way to do this automatically.</p>
  
  <p>Is there a way of telling <code>ggplot</code> to calculate breaks and labels automatically, but just have fewer, say at the minimum, maximum and zero point?</p>
  
  <p><em>EDIT:</em> Ideally, I don't want to specify the minimum and maximum points, but somehow tap into the built-in ggplot training of scales, and use the default calculated scale limits.</p>