Show each category as a percent of its city revenue

Question

The city dashboard shows revenue mix, not absolute revenue.

Write `share(df)` that returns a DataFrame with `city`, `category` and `pct` — each category's share of that city's total revenue as a percentage rounded to 1 decimal — sorted by city then descending share.

Accepted Answer

Step 1: Aggregate to one row per city/category first — the numerator of the share. Step 2: `groupby('city')['amount'].transform('sum')` broadcasts each city's total back onto every one of its rows, which is what makes the division a single vectorised step. Step 3: Multiply by 100 and round once, at the end, so the percentages still add up to 100 per city. Step 4: Sorting by city then descending share puts the dominant category first, the way the dashboard reads.

Show each category as a percent of its city revenue

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