d3 donut chart update with new csv dataset - d3.js

Question

Really struggling to get the donut chart updated with new data coming from several csv files.
How can I update the chart with the new csv file? Im using setInterval() to circulate the array of files.
My code:
var updateChart = function(){}
var width = 360;
var height = 360;
var radius = Math.min(width, height) / 2;
var donutWidth = 75;
var legendRectSize = 18;
var legendSpacing = 4;
var color = d3.scale.category20b();
var svg = d3.select('#chart')
.append('svg')
.attr('width', width)
.attr('height', height)
.append('g')
.attr('transform', 'translate(' + (width / 2) +
',' + (height / 2) + ')');
var arc = d3.svg.arc()
.innerRadius(radius - donutWidth)
.outerRadius(radius);
var pie = d3.layout.pie()
.value(function(d) { return d.population; })
.sort(null);
d3.csv('data.csv', function(error, dataset) {
dataset.forEach(function(d) {
d.population = +d.population;
}); /
var path = svg.selectAll('path')
.data(pie(dataset))
.enter()
.append('path')
.attr('d', arc)
.attr('fill', function(d, i) {
return color(d.data.age);
});
var legend = svg.selectAll('.legend')
.data(color.domain())
.enter()
.append('g')
.attr('class', 'legend')
.attr('transform', function(d, i) {
var height = legendRectSize + legendSpacing;
var offset = height * color.domain().length / 2;
var horz = -2 * legendRectSize;
var vert = i * height - offset;
return 'translate(' + horz + ',' + vert + ')';
});
legend.append('rect')
.attr('width', legendRectSize)
.attr('height', legendRectSize)
.style('fill', color)
.style('stroke', color);
legend.append('text')
.attr('x', legendRectSize + legendSpacing)
.attr('y', legendRectSize - legendSpacing)
.text(function(d) { return d; });
});
THE CSV FORMAT:
age,population
Cumulative,2704659
Cumulative Prev,4499890