This example shows stacked bar charts of population counts by age group and state for selected years and columns, with values labeled above each bar. The chart updates with smooth transitions when the user changes the year, column, or toggles sorting. Built with React and D3 v5, it uses d3.csv to load data, d3.scaleBand, d3.scaleLinear, d3.stack, and transition.duration to animate bar heights and positions. The SVG renders all bars and axes dynamically.