title: How to plot 3D graphs with ggplotly?
body: <p>I am running the following example from this <a href="http://blog.revolutionanalytics.com/2014/11/3-d-plots-with-plotly.html" rel="nofollow noreferrer">blog post</a>
  to draw a 3D chart. The code runs without any errors but the output is not as expected.
  Here is the code</p>
  
  <pre><code>library(plotly)
  pp &lt;- function (n,r=4) {
      x &lt;- seq(-r*pi, r*pi, len=n)
      df &lt;- expand.grid(x=x, y=x)
      df$r &lt;- sqrt(df$x^2 + df$y^2)
      df$z &lt;- cos(df$r^2)*exp(-df$r/6)
      df
  }
  qplot(x, y, data=pp(100), geom="tile", fill=z)
  ggplotly()
  </code></pre>
  
  <p>And here is what I would expect
  <a href="https://i.stack.imgur.com/sbdvA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/sbdvA.png" alt="enter image description here"></a></p>