Duration Histogram

This chart shows a histogram of a log-normal distribution of time durations. The data is randomly generated: each value is a number representing a duration measured in minutes. The values are then binned at regular intervals using D3’s histogram layout. A custom tick format for the x-axis converts these numbers to dates before passing them through a d3.time.format. The x-axis uses a linear scale, such that the tick values appear in-between bars; this provides better indication that each bar represents the count of values between its surrounding tick values.

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

body {
  font: 10px sans-serif;
}

.bar rect {
  fill: steelblue;
  shape-rendering: crispEdges;
}

.bar text {
  fill: #fff;
}

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

</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>

// Generate a log-normal distribution with a median of 30 minutes.
var values = d3.range(1000).map(d3.random.logNormal(Math.log(30), .4));

// Formatters for counts and times (converting numbers to Dates).
var formatCount = d3.format(",.0f"),
    formatTime = d3.time.format("%H:%M"),
    formatMinutes = function(d) { return formatTime(new Date(2012, 0, 1, 0, d)); };

var margin = {top: 10, right: 30, bottom: 30, left: 30},
    width = 960 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var x = d3.scale.linear()
    .domain([0, 120])
    .range([0, width]);

// Generate a histogram using twenty uniformly-spaced bins.
var data = d3.layout.histogram()
    .bins(x.ticks(20))
    (values);

var y = d3.scale.linear()
    .domain([0, d3.max(data, function(d) { return d.y; })])
    .range([height, 0]);

var xAxis = d3.svg.axis()
    .scale(x)
    .orient("bottom")
    .tickFormat(formatMinutes);

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 + ")");

var bar = svg.selectAll(".bar")
    .data(data)
  .enter().append("g")
    .attr("class", "bar")
    .attr("transform", function(d) { return "translate(" + x(d.x) + "," + y(d.y) + ")"; });

bar.append("rect")
    .attr("x", 1)
    .attr("width", x(data[0].dx) - 1)
    .attr("height", function(d) { return height - y(d.y); });

bar.append("text")
    .attr("dy", ".75em")
    .attr("y", 6)
    .attr("x", x(data[0].dx) / 2)
    .attr("text-anchor", "middle")
    .text(function(d) { return formatCount(d.y); });

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

</script>

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