How can I split an ordinal axis in d3? - d3.js

Question

The following is my draw axis code:
var seasons = ["summer", "winter", "fall", "spring"];
var margin = {top:80, right:30, bottom:30, left:30},
width = 1200 - margin.right - margin.left,
height = 800 - margin.top - margin.bottom;
var x = d3.scale.ordinal()
.domain(seasons)
.rangeRoundBands([0, width], 0.9);
xAxis = d3.svg.axis()
.scale(x)
.tickSize(4, 6)
.tickPadding(6)
.orient("bottom");
var svg = d3.select("body").append("svg")
.attr("width", width + margin.left + margin.right)
.attr("height", height + margin.top + margin.bottom)
.append("g")
.attr("transform", "translate(" + margin.left + "," + margin.top + ")");
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
</script>
However, the tickPadding function does now introduce a space between the ordinal axis categories.
More specifically, I want that each of the summer, winter, fall and spring parts of the axis are separate from each other, sort of like dashed line. How can I get this?

Answer 1

I don't know of any way built into the d3 axis to accomplish this, but you can remove the path it draws and replace it with a dashed line, like so:
// Draw the axis, as you currently are
var axisElem = svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
// Remove the line
axisElem.selectAll("path.domain").remove();
// Figure out how big each dash should be
var gapFraction = 0.1; // The portion of the line that should be a gap
var total = x(seasons[1]) - x(seasons[0]);
var dash = total * (1 - gapFraction);
var gap = total * gapFraction;
// Draw the dashed line
axisElem.append("line")
.classed("domain", true)
.attr("x1", x(seasons[0]) - dash / 2 + gap / 2)
.attr("x2", x(seasons[seasons.length - 1]) + dash / 2 - gap / 2)
.attr("y1", 0)
.attr("y2", 0)
.attr("stroke", "black")
.attr("stroke-dasharray", dash + "," + gap);