title: customizing strip of grids in ggplot2 in rpy2
body: <p>I'm trying to change the background colors of strips on top of facet grids/facet wraps in ggplot2 and also remove their bounding boxes (i.e. just show the labels). It seems that this require <code>element_rect</code> which is not defined in rpy2 -- how can its constructor be defined? Or is there an alternative way of doing this without <code>element_rect</code>? I tried:</p>
  
  <pre><code>my_plot += theme(**{'strip.background': element_blank()})
  </code></pre>
  
  <p>but it does not work, giving the error:</p>
  
  <pre><code>rpy2.rinterface.RRuntimeError: Error in (function (el, elname)  : 
    Element panel.background must be a element_rect object.
  </code></pre>
  
  <p>also,</p>
  
  <pre><code>from rpy2.robjects.lib.ggplot2 import element_rect
  </code></pre>
  
  <p>fails with an import error. how can this be done? </p>