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@phil-pedruco
Created August 19, 2014 19:45
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Plotting a bell (Gaussian) curve in d3
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>Normal Plot</title>
<meta name="description" content="">
<script src="http://d3js.org/d3.v3.min.js" charset="utf-8"></script>
<style type="text/css">
body {
font: 10px sans-serif;
}
.axis path,
.axis line {
fill: none;
stroke: #000;
shape-rendering: crispEdges;
}
/*.x.axis path {
display: none;
}*/
.line {
fill: none;
stroke: steelblue;
stroke-width: 1.5px;
}
</style>
</head>
<body>
</body>
<script type="text/javascript">
//setting up empty data array
var data = [];
getData(); // popuate data
// line chart based on http://bl.ocks.org/mbostock/3883245
var margin = {
top: 20,
right: 20,
bottom: 30,
left: 50
},
width = 960 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
var x = d3.scale.linear()
.range([0, width]);
var y = d3.scale.linear()
.range([height, 0]);
var xAxis = d3.svg.axis()
.scale(x)
.orient("bottom");
var yAxis = d3.svg.axis()
.scale(y)
.orient("left");
var line = d3.svg.line()
.x(function(d) {
return x(d.q);
})
.y(function(d) {
return y(d.p);
});
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(d3.extent(data, function(d) {
return d.q;
}));
y.domain(d3.extent(data, function(d) {
return d.p;
}));
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
svg.append("g")
.attr("class", "y axis")
.call(yAxis);
svg.append("path")
.datum(data)
.attr("class", "line")
.attr("d", line);
function getData() {
// loop to populate data array with
// probabily - quantile pairs
for (var i = 0; i < 100000; i++) {
q = normal() // calc random draw from normal dist
p = gaussian(q) // calc prob of rand draw
el = {
"q": q,
"p": p
}
data.push(el)
};
// need to sort for plotting
//https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort
data.sort(function(x, y) {
return x.q - y.q;
});
}
// from http://bl.ocks.org/mbostock/4349187
// Sample from a normal distribution with mean 0, stddev 1.
function normal() {
var x = 0,
y = 0,
rds, c;
do {
x = Math.random() * 2 - 1;
y = Math.random() * 2 - 1;
rds = x * x + y * y;
} while (rds == 0 || rds > 1);
c = Math.sqrt(-2 * Math.log(rds) / rds); // Box-Muller transform
return x * c; // throw away extra sample y * c
}
//taken from Jason Davies science library
// https://github.com/jasondavies/science.js/
function gaussian(x) {
var gaussianConstant = 1 / Math.sqrt(2 * Math.PI),
mean = 0,
sigma = 1;
x = (x - mean) / sigma;
return gaussianConstant * Math.exp(-.5 * x * x) / sigma;
};
</script>
</html>
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