D3轴标记

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).

In the new D3js version (version 3 onwards), when you create a chart axis via d3.svg.axis() function you have access to two methods called tickValues and tickFormat which are built-in inside the function so that you can specifies which values you need the ticks for and in what format you want the text to appear:

var formatAxis = d3.format("  0");
var axis = d3.svg.axis()
.scale(xScale)
.tickFormat(formatAxis)
.ticks(3)
.tickValues([100, 200, 300]) //specify an array here for values
.orient("bottom");

If you want the y-axis label in the middle of the y-axis like I did:

1. Rotate text 90 degrees with text-anchor middle
2. Translate the text by its midpoint
   • x position: to prevent overlap of y-axis tick labels (-50)
   • y position: to match the midpoint of the y-axis (chartHeight / 2)

Code sample:

var axisLabelX = -50;
var axisLabelY = chartHeight / 2;


chartArea
.append('g')
.attr('transform', 'translate(' + axisLabelX + ', ' + axisLabelY + ')')
.append('text')
.attr('text-anchor', 'middle')
.attr('transform', 'rotate(-90)')
.text('Y Axis Label')
;

This prevents rotating the whole coordinate system as mentioned by lubar above.

D3 provides a pretty low-level set of components that you can use to assemble charts. You are given the building blocks, an axis component, data join, selection and SVG. It's your job to put them together to form a chart!

If you want a conventional chart, i.e. a pair of axes, axis labels, a chart title and a plot area, why not have a look at d3fc? it is an open source set of more high-level D3 components. It includes a cartesian chart component that might be what you need:

var chart = fc.chartSvgCartesian(
d3.scaleLinear(),
d3.scaleLinear()
)
.xLabel('Value')
.yLabel('Sine / Cosine')
.chartLabel('Sine and Cosine')
.yDomain(yExtent(data))
.xDomain(xExtent(data))
.plotArea(multi);


// render
d3.select('#sine')
.datum(data)
.call(chart);

You can see a more complete example here: https://d3fc.io/examples/simple/index.html

If you work in d3.v4, as suggested, you can use this instance offering everything you need.

You might just want to replace the X-axis data by your "days" but remember to parse string values correctly and not apply concatenate.

parseTime might as well do the trick for days scaling with a date format ?

d3.json("data.json", function(error, data) {
if (error) throw error;


data.forEach(function(d) {
d.year = parseTime(d.year);
d.value = +d.value;
});


x.domain(d3.extent(data, function(d) { return d.year; }));
y.domain([d3.min(data, function(d) { return d.value; }) / 1.005, d3.max(data, function(d) { return d.value; }) * 1.005]);


g.append("g")
.attr("class", "axis axis--x")
.attr("transform", "translate(0," + height + ")")
.call(d3.axisBottom(x));




g.append("g")
.attr("class", "axis axis--y")
.call(d3.axisLeft(y).ticks(6).tickFormat(function(d) { return parseInt(d / 1000) + "k"; }))
.append("text")
.attr("class", "axis-title")
.attr("transform", "rotate(-90)")
.attr("y", 6)
.attr("dy", ".71em")
.style("text-anchor", "end")
.attr("fill", "#5D6971")
.text("Population)");

fiddle with global css / js

chart.xAxis.axisLabel('Label here');

or

xAxis: {
axisLabel: 'Label here'
},