Stacked Bar Chart Generator

Create stacked bar charts from grouped segment values.

Stacked Bar Chart Generator builds grouped bars with segment composition so you can compare both totals and internal mix across categories. It is useful for quarterly revenue mix, channel contribution analysis, and cohort composition reporting where each group contains multiple parts. The tool accepts rows in `Group, Segment, Value` format, calculates each segment's share within its group, and renders a legend for clear interpretation. Invalid lines are skipped with feedback for correction. Use it when you need to compare group size and composition on the same chart.