title: passing values from different environments to ggplot aes()?
body: <p>I've got this as part of an RShiny app:</p>
  <pre><code>sizeToUse = eval(length(levels(factor(df2$Cluster))))
  ggplot(df2, aes(x=Noise, y = AvgC), colour=clusterCat) + geom_point(inherit.aes = FALSE, aes_string(color=clusterCat, size=sizeToUse)) 
  </code></pre>
  <p>clusterCat is a column in the df2 dataframe, but sizeToUse is a variable declared separately and single not vector valued. Is there a way to pass both one variable that a column to the data frame and another variable that is just out there in a higher environment to aes in ggplot? I realize I could add sizeToUse as a column in df2, but this seems quite inefficient.</p>