Question

In the example, http://mbostock.github.com/d3/ex/bubble.html:

In line 27:

.style("fill", function(d) { return fill(d.packageName); });

Where is fill() defined? I didn’t find it in d3.js either. And even if the package name is not a color, some random color is being assigned. How so?

Answer 1

Take a look at the very top of the snippet you linked:

var r = 960,
    format = d3.format(",d"),
    fill = d3.scale.category20c();

That third line is where fill is being defined. You can find the doc for category20c here:

https://github.com/mbostock/d3/wiki/Ordinal-Scales#wiki-category20