How to create a histogram using d3.js and crossfilter data?

Here's my demo (permalink, it may take a second to download).

I have several problems with this:

• The cross filter key does not reflect the upper bound. Therefore, the x axis is missing one step.

  

  I managed to fix this by getting one group step size ( group.all()[1] - group.all()[0]) and then adding it to d3.extent(group.all())[1]. Since this is a dirty fix, I did not include it in the demo version (maybe a data gap). What is a less dirty way to get the group step size / fix the x axis?

• There are uneven gaps between the bars. I cannot figure out how to fix x.scale mismatch with different datasets.

  

  , . , ( ) :

  bar_width = math.round(graph_width/data_length);
  graph_width = bar_width*data_length;
  

  x.scale , . ; - . ?

  x.scale , bar_width graph_width x.scale . , , x.scale , .