title: NVD3 / D3 Chart Time Axis : Grouped by Date Part
body: <p>Is there a simple way to format the date of a d3/nvd3 graph as displayed in the image below?</p>
  
  <p><img src="https://i.stack.imgur.com/Hci3q.png" alt="NVD3 Graph with Axes as Desired">
  i.e. Rather than displaying the whole date against each tick, have the date grouped by date part; so the year is only displayed once, with all months within that year listed above it, then those months with the days listed above them?</p>
  
  <p>I've Googled and at looked at the available D3 formatting options but have so far found no examples or solutions which works in this "grouped" way.</p>