Variable Width Bar Chart Kampy Expression

This simple bar chart is constructed from a TSV file storing the frequency of letters in the English language. The chart employs conventional margins and a number of D3 features:

d3.tsv - load and parse data
d3.format - format percentages
d3.scale.ordinal - x-position encoding
d3.scale.linear - y-position encoding
d3.max - compute domains
d3.svg.axis - display axes

forked from mbostock's block: Simple Bar Chart Kampy Expression

forked from grybnicky's block: Simple Bar Chart Kampy Expression

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.bar {
  fill: steelblue;
}

.bar:hover {
  fill: brown;
}

.axis {
  font: 10px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}

.x.axis path {
  display: "black";
}

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>
d3.tsv("data.tsv", type, function(error, data) {
  if (error) throw error;
var margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var x = d3.scale.linear()
    .rangeRound([0,width]);

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

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom")
    .ticks(5);

var yAxis = d3.svg.axis()
    .scale(y)
    .orient("left")
    .ticks(10);

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 + ")");

x.domain(data.map(function(d) { return d.geneNumber; }));
  y.domain([0, d3.max(data, function(d) { return d.Expression; })]);

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

svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Expression (RPKM)");

svg.selectAll(".bar")
      .data(data)
    .enter().append("rect")
      .attr("class", "bar")
      .attr("x", function(d) { return x(d.start); })
      .attr("width", function(d) {return 200*d.Expression;})
      .attr("y", function(d) { return y(d.Expression); })
      .attr("height", function(d) { return height - y(d.Expression); });
});

function type(d) {
  d.Expression = +d.Expression;
  return d;
}

</script>

https://d3js.org/d3.v3.min.js