Update Pattern and Data Flow
This example demonstrates the general update pattern in D3.js, where data joins control the enter, update, and exit phases of SVG circles. It shows how fruit shapes change over time: apples are eaten, replaced by lemons, or removed entirely. The code uses `selection.data`, `selection.enter`, `selection.merge`, and `selection.exit` with transitions for smooth animations. A `scaleOrdinal` maps fruit types to colors and radii, while random IDs serve as the key function. The visualization cycles through pre-scripted state changes every second, illustrating unidirectional data flow from a mutable array to rendered marks.