Ordinal line chart

Line chart adapted from mbostock's simple bar chart

<!DOCTYPE html>
<meta charset="utf-8">
<style>
.bar {
  fill: steelblue;
}
.bar:hover {
  fill: brown;
}
.axis--x path {
  display: none;
}
.line {
  fill: none;
  stroke: steelblue;
  stroke-width: 3px;
}
.circle {
  fill: steelblue;
}
</style>
<svg width="960" height="500"></svg>
<script src="https://d3js.org/d3.v4.min.js"></script>
<script>
var svg = d3.select("svg"),
    margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = +svg.attr("width") - margin.left - margin.right,
    height = +svg.attr("height") - margin.top - margin.bottom;
var x = d3.scaleBand().rangeRound([0, width]).padding(0.1),
    y = d3.scaleLinear().rangeRound([height, 0]);
var g = svg.append("g")
    .attr("transform", "translate(" + margin.left + "," + margin.top + ")");
d3.tsv("data.tsv", function(d) {
  d.frequency = +d.frequency;
  return d;
}, function(error, data) {
  if (error) throw error;

var line = d3.line()
    .x(function(d) { return x(d.letter); })
    .y(function(d) { return y(d.frequency); })

x.domain(data.map(function(d) { return d.letter; }));

y.domain([0, d3.max(data, function(d) { return d.frequency; })]);
  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(10, "%"))
    .append("text")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", "0.71em")
      .attr("text-anchor", "end")
      .text("Frequency");

g.append("path")
    .datum(data)
    .attr("class", "line")
    .attr("d", line);

g.selectAll("circle")
    .data(data)
  .enter().append("circle")
    .attr("class", "circle")
    .attr("cx", function(d) { return x(d.letter); })
    .attr("cy", function(d) { return y(d.frequency); })
    .attr("r", 4);
});
</script>

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