This example shows an interactive donut chart whose displayed metric changes when the user selects a radio button. The chart initially renders apple counts from a TSV file, then after two seconds automatically switches to orange counts, updating the arc angles accordingly. Using D3 v3, the code employs `d3.layout.pie` and `d3.svg.arc` to compute and draw SVG path arcs, while the `change` event handler redefines the pie’s value function and redraws the arcs. A `color` scale from `d3.scale.category20` assigns distinct fills to each segment.