var width = 460,
height = 300,
radius = Math.min(width, height) / 2;
var color = d3.scale.category20();
var pie = d3.layout.pie();
var arc = d3.svg.arc()
.innerRadius(radius - 100)
.outerRadius(radius - 50);
var svg = d3.select("#chart").append("svg")
.attr("width", width)
.attr("height", height)
.append("g")
.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");
var path = svg.selectAll("path")
.data(pie(dataset))
.enter().append("path")
.attr("fill", function(d, i) { return color(i); })
.attr("d", arc);