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I am using Mike Bostok's Block for brushing a scatterplot matrix.
I want to brush the diagonal plots of the matrix using an opacity number; middle of brush range opacity = 1 and opacity value = low on the sides of the brush range.
I couldn't find a hint online, besides this question, which does an identical action but using dc.js (with help of pretransition attribute).
Can this be achieved in d3?
Running fiddle
481
A scatter plot matrix is a grid (or matrix) of scatter plots used to visualize bivariate relationships between combinations of variables. Each scatter plot in the matrix visualizes the relationship between a pair of variables, allowing many relationships to be explored in one chart.
Interesting question.
Here's a code snippet that'll set opacity on the selected circles by their distance from the center of the selection. It does this on the brush end with a nice transition. Here's the relevant method:
function brushend(p) {
// reset opacity
svg.selectAll("circle").style('opacity', 1);
// if no brush then bail
if (brush.empty()) {
svg.selectAll(".hidden").classed("hidden", false);
return;
}
// some calculations
var e = brush.extent(),
xC = (e[1][0] + e[0][0]) / 2,
yC = (e[1][1] + e[0][1]) / 2,
// maxD is the maximum of the distance to the two edges
maxD = Math.max( Math.sqrt((xC - e[0][0])**2), Math.sqrt ((yC - e[0][1])**2) );
// those circles not hidden
svg.selectAll("circle:not(.hidden)")
.transition()
.duration(1000)
.style("opacity", function(d) {
// distance from furthest edge
var xD = Math.sqrt( (xC - d[p.x])**2 + (yC - d[p.y])**2 );
// set opacity as percent of distance
return (maxD - xD) / maxD;
});
}
Running Code:
<!DOCTYPE html>
<meta charset="utf-8">
<style>
svg {
font: 10px sans-serif;
padding: 10px;
}
.axis,
.frame {
shape-rendering: crispEdges;
}
.axis line {
stroke: #ddd;
}
.axis path {
display: none;
}
.cell text {
font-weight: bold;
text-transform: capitalize;
}
.frame {
fill: none;
stroke: #aaa;
}
circle {
fill-opacity: .7;
}
circle.hidden {
fill: #ccc !important;
}
.extent {
fill: #000;
fill-opacity: .125;
stroke: #fff;
}
</style>
<body>
<script src="//d3js.org/d3.v3.min.js"></script>
<script>
var width = 960,
size = 230,
padding = 20;
var x = d3.scale.linear()
.range([padding / 2, size - padding / 2]);
var y = d3.scale.linear()
.range([size - padding / 2, padding / 2]);
var xAxis = d3.svg.axis()
.scale(x)
.orient("bottom")
.ticks(6);
var yAxis = d3.svg.axis()
.scale(y)
.orient("left")
.ticks(6);
var color = d3.scale.category10();
d3.csv("https://gist.githubusercontent.com/mbostock/4063663/raw/13276d1a3d8e99e74c9fe33685da3afa6ed3a926/flowers.csv", function(error, data) {
if (error) throw error;
var domainByTrait = {},
traits = d3.keys(data[0]).filter(function(d) { return d !== "species"; }),
n = traits.length;
traits.forEach(function(trait) {
domainByTrait[trait] = d3.extent(data, function(d) { return d[trait]; });
});
xAxis.tickSize(size * n);
yAxis.tickSize(-size * n);
var brush = d3.svg.brush()
.x(x)
.y(y)
.on("brushstart", brushstart)
.on("brush", brushmove)
.on("brushend", brushend);
var svg = d3.select("body").append("svg")
.attr("width", size * n + padding)
.attr("height", size * n + padding)
.append("g")
.attr("transform", "translate(" + padding + "," + padding / 2 + ")");
svg.selectAll(".x.axis")
.data(traits)
.enter().append("g")
.attr("class", "x axis")
.attr("transform", function(d, i) { return "translate(" + (n - i - 1) * size + ",0)"; })
.each(function(d) { x.domain(domainByTrait[d]); d3.select(this).call(xAxis); });
svg.selectAll(".y.axis")
.data(traits)
.enter().append("g")
.attr("class", "y axis")
.attr("transform", function(d, i) { return "translate(0," + i * size + ")"; })
.each(function(d) { y.domain(domainByTrait[d]); d3.select(this).call(yAxis); });
var cell = svg.selectAll(".cell")
.data(cross(traits, traits))
.enter().append("g")
.attr("class", "cell")
.attr("transform", function(d) { return "translate(" + (n - d.i - 1) * size + "," + d.j * size + ")"; })
.each(plot);
// Titles for the diagonal.
cell.filter(function(d) { return d.i === d.j; }).append("text")
.attr("x", padding)
.attr("y", padding)
.attr("dy", ".71em")
.text(function(d) { return d.x; });
cell.call(brush);
function plot(p) {
var cell = d3.select(this);
x.domain(domainByTrait[p.x]);
y.domain(domainByTrait[p.y]);
cell.append("rect")
.attr("class", "frame")
.attr("x", padding / 2)
.attr("y", padding / 2)
.attr("width", size - padding)
.attr("height", size - padding);
cell.selectAll("circle")
.data(data)
.enter().append("circle")
.attr("cx", function(d) { return x(d[p.x]); })
.attr("cy", function(d) { return y(d[p.y]); })
.attr("r", 4)
.style("fill", function(d) { return "#4682b4"; });
}
var brushCell;
// Clear the previously-active brush, if any.
function brushstart(p) {
if (brushCell !== this) {
d3.select(brushCell).call(brush.clear());
x.domain(domainByTrait[p.x]);
y.domain(domainByTrait[p.y]);
brushCell = this;
}
}
// Highlight the selected circles.
function brushmove(p) {
var e = brush.extent();
svg.selectAll("circle").classed("hidden", function(d) {
return e[0][0] > d[p.x] || d[p.x] > e[1][0]
|| e[0][1] > d[p.y] || d[p.y] > e[1][1];
});
}
function brushend(p) {
// reset opacity
svg.selectAll("circle").style('opacity', 1);
// if no brush then bail
if (brush.empty()) {
svg.selectAll(".hidden").classed("hidden", false);
return;
}
// some calculations
var e = brush.extent(),
xC = (e[1][0] + e[0][0]) / 2,
yC = (e[1][1] + e[0][1]) / 2,
// maxD is the maximum of the distance to the two edges
maxD = Math.max( Math.sqrt((xC - e[0][0])**2), Math.sqrt ((yC - e[0][1])**2) );
// those circles not hidden
svg.selectAll("circle:not(.hidden)")
.transition()
.duration(1000)
.style("opacity", function(d) {
// distance from furthest edge
var xD = Math.sqrt( (xC - d[p.x])**2 + (yC - d[p.y])**2 );
// set opacity as percent of distance
return (maxD - xD) / maxD;
});
}
});
function cross(a, b) {
var c = [], n = a.length, m = b.length, i, j;
for (i = -1; ++i < n;) for (j = -1; ++j < m;) c.push({x: a[i], i: i, y: b[j], j: j});
return c;
}
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