Pandas

1. Reshaping Data
   • Reindexing
   • Pivot / Stack / Unstack / Melt
   • Combining Data (Merge, Join, Concatenate)

2. Advanced Indexing
   • Selecting (loc, iloc)
   • Indexing with isin / where / query

3. Missing Data
   • Drop / Fill / Replace NaN

4. Grouping & Aggregation
   • GroupBy操作
   • 聚合函数（mean, sum, transform）

5. MultiIndexing
   • 多层索引操作

6. Dates & Time
   • 日期处理与时间序列

7. Visualization
   • 基础绘图方法