title: How can I format axis labels with exponents with ggplot2 and scales?
body: <p>With the new version ggplot2 and scales, I can't figure out how to get axis label in scientific notation. For example:</p>
  
  <pre><code>x &lt;- 1:4
  y &lt;- c(0, 0.0001, 0.0002, 0.0003)
  
  dd &lt;- data.frame(x, y)
  
  ggplot(dd, aes(x, y)) + geom_point()
  </code></pre>
  
  <p>gives me</p>
  
  <p><img src="https://i.stack.imgur.com/jvLLM.png" alt="Example ggplot with scales"></p>
  
  <p>I'd like the axis labels to be 0, 5 x 10^-5, 1 x 10^-4, 1.5 x 10^-4, etc. I can't figure out the correct combination of <code>scale_y_continuous()</code> and <code>math_format()</code> (at least I think those are what I need). </p>
  
  <p><code>scale_y_log10()</code> log transforms the axis, which I don't want. <code>scale_y_continuous(label = math_format())</code> just gives me 10^0, 10^5e-5, etc. I see why the latter gives that result, but it's not what I'm looking for.</p>
  
  <p>I am using ggplot2_0.9.1 and scales_0.2.1</p>