This visualization demonstrates how to use D3.js data transformation techniques to summarize the classic Iris flower dataset. It computes the average sepal length for each iris species using `d3.flatRollup` and `d3.sum`, then displays the resulting summary as formatted JSON text in a `<pre>` element. The code loads data from a local CSV file with `d3.csvParse` and showcases commented-out examples of other transformations like `d3.bin`, `d3.extent`, and `d3.group`.