title: d3 donut chart update with new csv dataset
body: <p>Really struggling to get the donut chart updated with new data coming from several csv files.</p>
  <p>How can I update the chart with the new csv file? Im using setInterval() to circulate the array of files.</p>
  <p>My code:</p>
  <pre><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; });                       
  
      });  
  </code></pre>
  <p>THE CSV FORMAT:</p>
  <pre><code> age,population
   Cumulative,2704659
   Cumulative Prev,4499890
  </code></pre>