Learning about Histograms

Playing around with d3 v4 Histograms

Concepts

Histograms

TBA

Generating Data

Understanding Randomness

d3 offers different ways on generating randomness.

d3.randomUniform([min, ][max])

Using a uniform random number generator distributes a range of numbers evenly. Math.random() also uses the same distribution.

Looking at the first chart, we can see how flat the graph looks.

d3.randomBates()

Generating randomness

Documentation

Returns a function for generating random numbers with a Bates distribution with n independent variables.

Wolfram Alpha

Bates Distribution represents the distribution of a mean of n random variables uniformly distributed from 0 to 1.

d3.randomBates(1);
d3.randomBates(10);
d3.randomBates(100);

index.html

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

.bar rect {
  fill: steelblue;
}

.bar text {
  fill: #fff;
  font: 10px sans-serif;
}

</style>
<body>
<script src="https://d3js.org/d3.v4.0.0-alpha.50.min.js"></script>
<script>

var uniformData = d3.range(1000).map(d3.randomUniform(0, 1));
var normalData = d3.range(1000).map(d3.randomNormal(0.5, 0.15));
var logNormalData = d3.range(1000).map(d3.randomLogNormal(-1, 0.5));  
var batesData = d3.range(1000).map(d3.randomBates(10));
var irwinHallData = d3.range(1000).map(d3.randomIrwinHall(1.41));
var exponentialData = d3.range(1000).map(d3.randomExponential(4));
  
const chartWidth = 500;
const chartHeight = 300;
  
function createChart(data) {
	var formatCount = d3.format(",.0f");

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

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

  var bins = d3.histogram()
      .domain(x.domain())
      .thresholds(x.ticks(20))
      (data);

  var y = d3.scaleLinear()
      .domain([0, d3.max(bins, function(d) { return d.length; })])
      .range([height, 0]);

  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(bins)
    .enter().append("g")
      .attr("class", "bar")
      .attr("transform", function(d) { return "translate(" + x(d.x0) + "," + y(d.length) + ")"; });

  bar.append("rect")
      .attr("x", 1)
      .attr("width", x(bins[0].x1) - x(bins[0].x0) - 1)
      .attr("height", function(d) { return height - y(d.length); });

  bar.append("text")
      .attr("dy", ".75em")
      .attr("y", 6)
      .attr("x", (x(bins[0].x1) - x(bins[0].x0)) / 2)
      .attr("text-anchor", "middle")
      .text(d => formatCount(d.length));

  svg.append("g")
      .attr("class", "axis axis--x")
      .attr("transform", "translate(0," + height + ")")
      .call(d3.axisBottom(x));  
}
createChart(uniformData);
createChart(normalData);
createChart(logNormalData);
createChart(batesData);
createChart(irwinHallData);
createChart(exponentialData);
</script>

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