This example displays a static pie chart that categorizes daily ozone air-quality readings by AQI category, showing the number of distinct dates per category. Using D3 v7, the code loads a CSV dataset from a GitHub gist via `d3.csv`, aggregates the data into category-count pairs with JavaScript Sets, and renders the results as text. Although the page initially outputs “Hello D3 version 7” using `select('body').text()`, the pie chart itself is not drawn—only the computed data is prepared but never visualized. The visualization uses no SVG or canvas rendering, and the final output remains a simple text greeting.