score:1

You can do something like this:

0) Calculte the center of the path using the function below:

  function getMyCentroid(element) {
    var bbox = element.getBBox();
    return [bbox.x + bbox.width / 2, bbox.y + bbox.height / 2];
  }

1) Next select all path and calculate its center.

2) Append a text and position it at the center svg.append("text")

3) Set the text associated with the path like this .text(d3.select(d).data()[0].key);

  d3.selectAll(".layer")[0].forEach(function(d) {
    var centroid = getMyCentroid(d);
    svg.append("text").attr("x", centroid[0]).attr("y", centroid[1]).text(d3.select(d).data()[0].key);
  })

var format = d3.time.format("%m/%d/%y");

var margin = {top: 20, right: 30, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var x = d3.time.scale()
    .range([0, width]);

var y = d3.scale.linear()
    .range([height, 0]);

var z = d3.scale.category20c();

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom")
    .ticks(d3.time.days);

var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left");

var stack = d3.layout.stack()
    .offset("zero")
    .values(function(d) { return d.values; })
    .x(function(d) { return d.date; })
    .y(function(d) { return d.value; });

var nest = d3.nest()
    .key(function(d) { return d.key; });

var area = d3.svg.area()
    .interpolate("cardinal")
    .x(function(d) { return x(d.date); })
    .y0(function(d) { return y(d.y0); })
    .y1(function(d) { return y(d.y0 + d.y); });

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 + ")");

d3.csv("https://gist.githubusercontent.com/cyrilcherian/e6f56b1b9337142c0bde/raw/8b1728849e193db0e8b960ecb750062f4e0cb487/data.csv", function(error, data) {
  if (error) throw error;

  data.forEach(function(d) {
    d.date = format.parse(d.date);
    d.value = +d.value;
  });

  var layers = stack(nest.entries(data));

  x.domain(d3.extent(data, function(d) { return d.date; }));
  y.domain([0, d3.max(data, function(d) { return d.y0 + d.y; })]);

  svg.selectAll(".layer")
      .data(layers)
    .enter().append("path")
      .attr("class", "layer")
      .attr("d", function(d) { return area(d.values); })
      .style("fill", function(d, i) { return z(i); });

  svg.append("g")
      .attr("class", "x axis")
      .attr("transform", "translate(0," + height + ")")
      .call(xAxis);

  svg.append("g")
      .attr("class", "y axis")
      .call(yAxis);
  
  function getMyCentroid(element) {
    var bbox = element.getBBox();
    return [bbox.x + bbox.width / 2, bbox.y + bbox.height / 2];
  }
    d3.selectAll(".layer")[0].forEach(function(d) {
    var centroid = getMyCentroid(d);
    svg.append("text").attr("x", centroid[0]).attr("y", centroid[1]).text(d3.select(d).data()[0].key).style("fill", "red");
  })
  
});
body {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>

Hope this helps!


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