title: ggvis, error in function( ) : attempt to apply non-function : post sessionInfo()
body: <pre><code>library("dplyr") 
  library("ggvis")
  mtcars %&gt;% ggvis(~wt,~mpg) %&gt;% layer_points()
  sessionInfo()
  </code></pre>
  
  <p>I posted sessionInfo() because I have an Error in (function ()  : attempt to apply non-function. 
  When I use R markdown and run, it works. It has error all the time, when I run it in R. </p>