title: Can't add geom_point to line plot with stat_count
body: <p>I have a df where I have made a nice line plot using <code>stat_count</code>, but when I try to add <code>geom_point</code> it won't work. </p>
  
  <p>Without the last part (<code>geom_point(size=2)</code>) it produces a line plot, but with it I get error: </p>
  
  <blockquote>
    <p>Don't know how to automatically pick scale for object of type
    function. Defaulting to continuous. Error: Column <code>y</code> must be a 1d
    atomic vector or a list</p>
  </blockquote>
  
  <pre><code>df &lt;- data.frame("id" = c(1, 1, 1, 2, 2, 3, 3, 3, 4, 4), 
                   "bowl" = c("red", "red", "red","green", "green", "green",  
                              "green", "green", "red", "red"),
                   "year"=c(2001:2003, 2002:2003, 2001:2003, 2001:2002))
  
  library(dplyr)
  library(ggplot2)
  df %&gt;% 
    ggplot(aes(x=year, y=count, colour=bowl)) +
    stat_count(geom = "line", 
               aes(y=..count..))+
    geom_point(size=2) 
  </code></pre>
  
  <p>I suspect there's just a small adjustment to be made, but I can't seem to find it on my own. </p>