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mbostock/.block

Last active Feb 9, 2016
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Hashing Points
license: gpl-3.0

Testing a possible hash function for points (pairs of floating-point coordinates).

<!DOCTYPE html>
<meta charset="utf-8">
<style>
.bar {
fill: steelblue;
}
.axis line,
.axis path {
fill: none;
stroke: #000;
shape-rendering: crispEdges;
}
.axis text {
display: none;
}
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>
var m = 256,
bins = d3.range(m).map(function() { return 0; });
var margin = {top: 20, right: 30, bottom: 30, left: 40},
width = 960 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
var x = d3.scale.ordinal()
.domain(d3.range(m))
.rangeBands([0, width], .1);
var y = d3.scale.linear()
.range([height, 0]);
var xAxis = d3.svg.axis()
.scale(x)
.orient("bottom")
.tickSize(4, 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 + ")");
svg.append("g")
.attr("class", "bar")
.selectAll("rect")
.data(bins)
.enter().append("rect")
.attr("y", height)
.attr("width", x.rangeBand())
.attr("x", function(d, i) { return x(i); });
svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
var bars = svg.selectAll(".bar rect")[0].map(d3.select);
d3.json("/mbostock/raw/4090846/us.json", function(error, us) {
if (error) throw error;
var collection = topojson.feature(us, us.objects.counties), points = [];
collection.features.forEach(function(f) {
var g = f.geometry;
if (g) switch (g.type) {
case "MultiPolygon": g.coordinates.forEach(polygon); break;
case "Polygon": g.coordinates.forEach(ring); break;
}
});
function polygon(coordinates) {
coordinates.forEach(ring);
}
function ring(coordinates) {
coordinates.forEach(point);
}
function point(coordinates) {
points.push(coordinates);
}
y.domain([0, points.length / m * 2]);
d3.timer(function() {
for (var k = 0, p; k < 100; ++k) {
if (!(p = points.pop())) return true;
var i = Math.abs(hash2(p[0], p[1]) % m), j = ++bins[i];
bars[i].attr("y", y(j)).attr("height", height - y(j));
}
});
});
var buffer = new ArrayBuffer(8),
floats = new Float64Array(buffer),
ints = new Int32Array(buffer);
function hash1(x) {
floats[0] = x;
x = ints[1] ^ ints[0];
x ^= (x >>> 20) ^ (x >>> 12);
x ^= (x >>> 7) ^ (x >>> 4);
return x;
}
function hash2(x, y) {
return (hash1(x) + 31 * hash1(y)) | 0;
}
</script>
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