title: Line plus bar chart in ggplot2
body: <p>I am trying to plot line plus bar chart using ggplot but I am getting the error "Error: ggplot2 doesn't know how to deal with data of class uneval"</p>
  
  <pre><code>require(ggplot2)    
  df.1 &lt;- data.frame(x = c(1:5), y = rnorm(5))
  df.2 &lt;- data.frame(x = c(1:10), y = runif(10))
  
  p &lt;- ggplot(df.1, aes(x=x, y=y)) + 
      geom_bar(stat = "identity") +
      geom_line(df.2, aes(x=x, y=y))
  </code></pre>
  
  <p>x-axis scale for both data frames is always same but one needs to be plotted as line chart while the other needs to be plotted as bar chart. It seems to me that two data frames are not supported in ggplot2. Is there a work around to overcome this?</p>
  
  <p>I tried using nvd3 through rCharts but is doesn't seem to support linePlusBarChart as of now.</p>
  
  <p>Thanks in advance!!!</p>