title: R - contour plot in three variables
body: <p>I'd like to know if there is a way to produce plots in R function similar to Mathematica's <a href="http://reference.wolfram.com/language/ref/ContourPlot3D.html" rel="nofollow">ContourPlot3D</a> function? Basically, it allows you to plot a 3D surface at values of <strong><em>f</em></strong>, where <strong><em>f</em></strong> is an implicit function in three variables. The example from Mathematica: <strong><em>f(x,y,z) = x^3 + y^2 + z^2</em></strong>.  </p>
  
  <pre><code>x &lt;- y &lt;- z &lt;- seq(-2, 2, by=0.2)
  grid &lt;- expand.grid(x=x,y=y,z=z)
  grid$f &lt;- x^3 + y^2 + z^2
  </code></pre>