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Last active April 8, 2016 22:25
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Duration Histogram
license: gpl-3.0

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.

See also this histogram of an Irwin–Hall distribution.

<!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>
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