d3 axis labeling

How do I add text labels to axes in d3?

For instance, I have a simple line graph with an x and y axis.

On my x-axis, I have ticks from 1 to 10. I want the word "days" to appear underneath it so people know the x axis is counting days.

Similarly, on the y-axis, I have the numbers 1-10 as ticks, and I want the words "sandwiches eaten" to appear sideways.

Is there a simple way to do this?

Solution

Axis labels aren't built-in to D3's axis component, but you can add labels yourself simply by adding an SVG text element. A good example of this is my recreation of Gapminder’s animated bubble chart, The Wealth & Health of Nations. The x-axis label looks like this:

svg.append("text")
    .attr("class", "x label")
    .attr("text-anchor", "end")
    .attr("x", width)
    .attr("y", height - 6)
    .text("income per capita, inflation-adjusted (dollars)");

And the y-axis label like this:

svg.append("text")
    .attr("class", "y label")
    .attr("text-anchor", "end")
    .attr("y", 6)
    .attr("dy", ".75em")
    .attr("transform", "rotate(-90)")
    .text("life expectancy (years)");

You can also use a stylesheet to style these labels as you like, either together (.label) or individually (.x.label, .y.label).