7-Likert scale results visualization D3 v4

A visualization of a 7 Likert scale using d3v4. Based on the diverging stacked bar chart example from mbostock

<!DOCTYPE html>
<meta charset="utf-8">
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script src="https://d3js.org/d3-color.v1.min.js"></script>
<script src="https://d3js.org/d3-interpolate.v1.min.js"></script>
<script src="https://d3js.org/d3-scale-chromatic.v1.min.js"></script>

<script src="./d3-legend.js"></script>
<style>
body {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
}
.legend {
  font-size: 10pt;
}
</style>

var LIKERT_MAX = 7;
var LIKERT_NEUTRAL = Math.round(LIKERT_MAX/2);

var formatPercent = d3.format("+.0%")

var svg = d3.select("svg"),
    margin = {top: 20, right: 180, bottom: 30, left: 60},
    width = +svg.attr("width"),
    height = +svg.attr("height");

var y = d3.scaleBand()
    .padding(0.1)
    .rangeRound([margin.top, height - margin.bottom]);

var x = d3.scaleLinear()
    .rangeRound([margin.left, width - margin.right]);

var z = d3.scaleSequential(d3.interpolateRdBu)
  .domain([-3,3]);

d3.csv("results.csv", function (err, data) {
  if (err) throw err;
  var totalAnswers = d3.max(data, function (q) {
    return d3.range(1, LIKERT_MAX+1).reduce(function (acc, val) {
      q[val]=+q[val];
      return acc+ q[val]
    }, 0);
  });
  var series = d3.stack()
      .keys(d3.range(1,LIKERT_MAX+1))
      .offset(stackOffsetLikert)
      (data);

y.domain(data.map(function(d) { return d.question; }));
  x.domain([d3.min(series, stackMin), d3.max(series, stackMax)]);

svg.append("g")
    .selectAll("g")
    .data(series)
    .enter().append("g")
      .attr("fill", function(d) { return z(+d.key - LIKERT_NEUTRAL); })
    .selectAll("rect")
    .data(function(d) { return d; })
    .enter().append("rect")
      .attr("height", y.bandwidth)
      .attr("y", function(d) { return y(d.data.question); })
      .attr("x", function(d) { return x(d[0]); })
      .attr("width", function(d) { return x(d[1]) - x(d[0]); })

svg.append("g")
      .attr("transform", "translate(0," + (height-margin.bottom) + ")")
      .call(d3.axisBottom(x).tickFormat(function (d) {return formatPercent(Math.abs(d/totalAnswers));}));

svg.append("g")
      .attr("transform", "translate(" + margin.left + ",0)")
      .call(d3.axisLeft(y));

addLegend(z);
  // var linear = d3.scaleLinear()
  // .domain([0,10])
  // .range(["rgb(46, 73, 123)", "rgb(71, 187, 94)"]);
  // addLegend(linear)

function stackMin(serie) {
    return d3.min(serie, function(d) { return d[0]; });
  }

function stackMax(serie) {
    return d3.max(serie, function(d) { return d[1]; });
  }

// Assumes that the series include answers in the LIKERT_MAX Likert scale (default 7), therefore
  // 1-3 are negative, 4 is neutral and 5-7 are positive
  function stackOffsetLikert(series, order) {
    if (!((n = series.length) > 1)) return;
    for (var i, j = 0, d, dy, yp, yn, n, m = series[order[0]].length; j < m; ++j) {
      // Stack the neutral and positive values
      for (yp = yn = 0, i = LIKERT_NEUTRAL-1; i < n; ++i) {
        dy = (d = series[order[i]][j])[1] - d[0];

if (i=== (LIKERT_NEUTRAL-1)) {
          //neutral goes centered in the middle
          d[0] = yp -dy/2, d[1] = yp += dy/2;
        } else {
          d[0] = yp, d[1] = yp += dy;
        }
      }
      // Now stack the negative values
      for (yp = yn = 0, i = LIKERT_NEUTRAL-1; i >= 0 ; --i) {
        dy = (d = series[order[i]][j])[1] - d[0];
        if (i=== (LIKERT_NEUTRAL-1)) {
          yp -= dy/2;
        } else
        if (i <(LIKERT_NEUTRAL-1)) {
          d[1] = yp, d[0] = yp -= dy;
        }
      }
    }
  }
})

function addLegend(z) {
  svg.append("g")
    .attr("class", "legend")
    .attr("transform", "translate("+ (width - margin.right + 10 ) + ",20)");

var colorLegend = d3.legendColor()
      .labelFormat(d3.format(".2f"))
      // .labels(d3.legendHelpers.thresholdLabels)
      .cells(LIKERT_MAX)
      .title("Answers")
      .labels(["Significantly worse", "Worse", "Somewhat worse", "Equal", "Somewhat better", "Better", "Significantly better"])
      .scale(z);

svg.select(".legend")
    .call(colorLegend);
}

</script>

https://d3js.org/d3.v4.min.js

https://d3js.org/d3-color.v1.min.js

https://d3js.org/d3-interpolate.v1.min.js

https://d3js.org/d3-scale-chromatic.v1.min.js

https://cdnjs.cloudflare.com/ajax/libs/d3-legend/2.22.0/d3-legend.js