d3 donut chart transistion change - d3.js

Question

Another d3 newbie question here.
I am trying to transition change a donut chart with grouped nested data. Here's what I have now.
http://bricbracs.com/test/
So when I click on a segment arc like New York it will update with data from the dept column with a nested function so I get this. I am close. I have the data grouped. I need help redrawing the donut.
http://bricbracs.com/test1/
Here is a csv file.
status,dept,city,points
temp,finance,New York,33
contract,HR,London,12
contract,HR,New York,11
casual,shop,London,43
contract,shop,Paris,51
temp,finance,London,7
contract,office,New York,61
contract,shop,London,31
temp,office,New York,16
contract,office,London,19
temp,finance,London,7
contract,office,New York,61
contract,sales,London,31
temp,finance,New York,16
contract,sales,Paris,19
Here is the d3 script. Thanks in advance.
<script>
var width = 960,
height = 500,
radius = Math.min(width, height) / 2;
var color = d3.scale.category20();
var arc = d3.svg.arc()
.outerRadius(radius - 10)
.innerRadius(radius - 70);
var pie = d3.layout.pie()
.sort(null)
.value(function(d) {
return d.values;
});
var svg = d3.select("body").append("svg")
.attr("width", width)
.attr("height", height)
.append("g")
.attr("transform", "translate(" + width / 2 + "," + height / 2 + ")");
svg.style("cursor","pointer")
d3.csv("data.csv", function(error, data) {
var data = d3.nest()
.key(function(d) {
return d.city;
})
.rollup(function(d) {
return d3.sum(d, function(g) {
return g.points;
});
}).entries(data);
var g = svg.selectAll(".arc")
.data(pie(data))
.enter().append("g")
.attr("class", "arc");
g.append("path")
.attr("d", arc)
.attr("stroke", "white")
.attr("stroke-width", 0.5)
.style("fill", function(d) {
return color(d.data.key);
})
.on("mouseover", function (d) {
d3.select("#tooltip")
.style("left", d3.event.pageX + "px")
.style("top", d3.event.pageY + "px")
.style("opacity", .75)
.select("#value")
.text(d.value.toLocaleString())
document.getElementById("demo").innerHTML =d.data.key
})
.on("mouseout", function () {
d3.select("#tooltip")
.style("opacity", 0);
console.log("OUT")
})
.on("mousemove", function () {
d3.select("#tooltip")
.style("left", (d3.event.pageX +20) + "px")
.style("top", d3.event.pageY + "px+50")
})
.on("click", function() {
change()
});
g.append("text")
.attr("transform", function(d) {
var c = arc.centroid(d),
x = c[0],
y = c[1],l
h = Math.sqrt(x*x + y*y);
return "translate(" + arc.centroid(d) + ")";
})
//.attr("dy", "1em")
.style("text-anchor", "middle")
.text(function(d) {
return d.data.key
})
function change() {
var data = d3.nest()
.key(function(d) {
return d.dept;
})
.rollup(function(d) {
return d3.sum(d, function(g) {
return g.points;
});
}).entries(data);
var path = svg.selectAll("path");
path = path.data(pie(data), function(d) { return d.data.key; })
path.enter().append("path").attr("fill", function(d) {return color(d.data.key); })
path.exit().remove()
path.attr("d", arc)
}
});