Label placement in d3 radial bar chart

Question

Here in my d3 radial chart, I am trying to get the label text just above the segment arcs instead of keeping outside the outer circle.

Fiddle

Answer 1

We can set the position of the <defs>'s paths using the same data you used to create the arcs.

First, let's create an enter selection:

var labels = svg.selectAll("foo")
    .data(data)
    .enter()
    .append("g")
    .classed("labels", true);

Then, we append the paths using the barScale for each value (hardcoded padding of 4px here):

labels.append("def")
    .append("path")
    .attr("id", (d, i) => "label-path" + i)
    .attr("d", d => "m0 " + -(barScale(d.value) + 4) +
        " a" + (barScale(d.value) + 4) + " " +
        (barScale(d.value) + 4) + " 0 1,1 -0.01 0");

Please notice that we have to use unique IDs. Then, we change the IDs in the text-paths:

.attr("xlink:href", (d, i) => "#label-path" + i)

Here is your updated fiddle: https://jsfiddle.net/qt3e0rex/

And the same code in the Stack snippet:

var width = 360,
    height = 300,
    barHeight = height / 2 - 40;

var formatNumber = d3.format("s");

var color = d3.scale.ordinal()
    .range(["#F15D5D", "#FAD64B"]);

var svg = d3.select('body').append("svg")
    .attr("width", width)
    .attr("height", height)
    .attr('class', 'radial')
    .append("g")
    .attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");

var data = [{
    "name": "ABC",
    "value": 4
}, {
    "name": "XYZ",
    "value": 5
}, {
    "name": "DEF",
    "value": 2
}, {
    "name": "GHI",
    "value": 3
}, {
    "name": "JKL",
    "value": 1
}];

data.sort(function(a, b) {
    return b.value - a.value;
});

var extent = [0, d3.max(data, d => d.value)];
var barScale = d3.scale.linear()
    .domain(extent)
    .range([0, barHeight]);

var keys = data.map(function(d, i) {
    return d.name;
});
var numBars = keys.length;

// X scale
var x = d3.scale.linear()
    .domain(extent)
    .range([0, -barHeight]);

// X axis
var xAxis = d3.svg.axis()
    .scale(x).orient("left")
    .ticks(3)
    .tickFormat(formatNumber);

// Inner circles
var circles = svg.selectAll("circle")
    .data(x.ticks(5))
    .enter().append("circle")
    .attr("r", function(d) {
        return barScale(d);
    })
    .style("fill", "none")
    //.style("stroke", "black")
    //.style("stroke-dasharray", "2,2")
    .style("stroke-width", ".5px");

// Create arcs
var arc = d3.svg.arc()
    .startAngle(function(d, i) {
        var a = (i * 2 * Math.PI) / numBars;
        var b = ((i + 1) * 2 * Math.PI) / numBars;
        var d = (b - a) / 4;
        var x = a + d;
        var y = b - d;

        return x; //(i * 2 * Math.PI) / numBars; 
    })
    .endAngle(function(d, i) {
        var a = (i * 2 * Math.PI) / numBars;
        var b = ((i + 1) * 2 * Math.PI) / numBars;
        var d = (b - a) / 4;
        var x = a + d;
        var y = b - d;
        return y; //((i + 1) * 2 * Math.PI) / numBars; 
    })
    .innerRadius(0);

// Render colored arcs
var segments = svg.selectAll("path")
    .data(data)
    .enter().append("path")
    .each(function(d) {
        d.outerRadius = 0;
    })
    .style("fill", function(d) {
        return color(d.name);
    })
    .attr("d", arc);

// Animate segments
segments.transition().ease("elastic").duration(1000).delay(function(d, i) {
        return (25 - i) * 50;
    })
    .attrTween("d", function(d, index) {
        var i = d3.interpolate(d.outerRadius, barScale(+d.value));
        return function(t) {
            d.outerRadius = i(t);
            return arc(d, index);
        };
    });

// Outer circle
svg.append("circle")
    .attr("r", barHeight)
    .classed("outer", true)
    .style("fill", "none")
    //.style("stroke", "black")
    .style("stroke-width", ".5px");

// Apply x axis
svg.append("g")
    .attr("class", "x axis")
    .call(xAxis);

// Labels
var labelRadius = barHeight * 1.025;

var labels = svg.selectAll("foo")
    .data(data)
    .enter()
    .append("g")
    .classed("labels", true);

labels.append("def")
    .append("path")
    .attr("id", (d, i) => "label-path" + i)
    .attr("d", d => "m0 " + -(barScale(d.value) + 4) + " a" + (barScale(d.value) + 4) + " " + (barScale(d.value) + 4) + " 0 1,1 -0.01 0");

labels.append("text")
    .style("text-anchor", "middle")
    .style("font-weight", "bold")
    .style("fill", function(d, i) {
        return "#555";
    })
    .append("textPath")
    .attr("xlink:href", (d, i) => "#label-path" + i)
    .attr("startOffset", function(d, i) {
        return i * 100 / numBars + 50 / numBars + '%';
    })
    .text(function(d) {
        return d.name.toUpperCase();
    });

body {
  background-color:#fff;
}
.axis path, .axis line {
		fill: none;
		shape-rendering: crispEdges;
	}

	.x.axis path {
		display: none;
	}
  
	.tick text, line {
			display:none;
		}
    
  circle {
    stroke:#ccc;
  }

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