title: What exactly does stat=identity mean in geom_bar ggplot?
body: <p>I'm working through someone else's work and having trouble understanding the purpose of this line of code:</p>
  
  <pre><code>ggplot(data, aes(x = Group, y = Value)) + geom_bar(stat="identity", position = "dodge", lwd = 1,  aes(fill = Group))
  </code></pre>
  
  <p>Here's an example of the data</p>
  
  <pre><code>   Group  Value
  1    A      20
  2    B      74
  3    B      50
  ...
  n    A      24
  </code></pre>
  
  <p>I think the purpose of the code used was to plot a bar graph summarising the value of group A and of group B. However I believe a bar is plotted for every element of group A and of group B, and all these bars overlap and only the maximum value of each group is shown.
  Is this the case?
  I think the aim was to plot a summary statistic, either the mean or median rather than plot all and only being able to see the maximum.</p>
  
  <p>If this is not what is happening I'd appreciate any help in understanding what the use of stat='identity' means as reading the documentation hasn't helped me much.</p>
  
  <p>Thank you</p>