These axes are styled in the manner of ggplot2, a plotting system for R. Two d3.svg.axis instances are used: one for the gray grid lines, and one for the black ticks and labels below the bottom of the chart area. The exit selection of a data-join is used to customize the appearance of minor ticks.
forked from mbostock's block: ggplot2-Style Axis
forked from lambrex's block: ggplot2-Style Axis
https://d3js.org/d3.v3.min.js