This example shows an interactive bar chart of coffee product sales, aggregating monthly units sold per product using d3.rollup and d3.sum. Built with React and D3 v7, the chart renders SVG bars that change fill color and stroke on click, with scales created via d3.scaleBand and d3.scaleLinear. Axes are drawn using d3.axisBottom and d3.axisLeft, with labels added through d3 selection joins. Data loads from a CSV file, and the chart resizes responsively using a ResizeObserver.