This example demonstrates data transformation using the Iris dataset, loading CSV data and computing the average sepal length for each species. The visualization displays the resulting summary as formatted JSON text. Built with D3 v7, the code uses `csvParse` to parse the data, `flatRollup` and `sum` to aggregate values, and `select` to render the output. The example also illustrates asynchronous data loading with `fetch` and state management through a custom `setState` pattern.