title: Plotting the average values for each level in ggplot2
body: <p>I'm using ggplot2 and am trying to generate a plot which shows the following data.</p>
  
  <pre><code>df=data.frame(score=c(4,2,3,5,7,6,5,6,4,2,3,5,4,8),
                age=c(18,18,23,50,19,39,19,23,22,22,40,35,22,16))
  str(df)
  df
  </code></pre>
  
  <p>Instead of doing a frequency plot of the variables (see below code), I want to generate a plot of the average values for each x value. So I want to plot the average score at each age level. At age 18 on the x axis, we might have a <strong>3</strong> on the y axis for score. At age 23, we might have an average score of <strong>4.5</strong>, and so forth (<strong>Edit</strong>: average values corrected). This would ideally be represented with a barplot.</p>
  
  <pre><code>ggplot(df, aes(x=factor(age), y=factor(score))) + geom_bar()
  Error: stat_count() must not be used with a y aesthetic.
  </code></pre>
  
  <p>Just not sure how to do this in R with ggplot2 and can't seem to find anything on such plots. Statisticially, I don't know if the plot I desire to plot is even the right thing to do, but that's a different store.</p>
  
  <p>Thanks!</p>