title: What does group do in the aes parameter of ggplot2
body: <p>Can someone please help explain what the group parameter does in ggplot2? I'm looking at a line of code that looks as follows:</p>
  
  <pre><code>ggplot(summarized.current.data, aes(x = GROUP_ID, y= Endpoint.Value, color = GROUP_ID, group = GROUP_ID))
  </code></pre>
  
  <p>On the bottom of my chart I correctly get group_id,  on the y-axis I get the endpoint value. It correctly colors them by group. But what does the "group = GROUP_ID" do? The charts do come out different but I can't quite figure out how.</p>