title: d3.js How to add lines to a bar chart
body: <p>I have a data set of 4 values. [a,b,c,d]. Currently they are displayed in a bar chart, for each value one bar. Now as values c and d are averages, i would like to display them as line behind the bars of a and b. Is this possible with d3? How can I switch between bar or line display within the same dataarray? </p>
  
  <p>Thanks for your help. </p>