Reshape Hierarchical Series with unstack() in Pandas

Question

Given a multi-index Series resulting from `df.groupby(['year', 'quarter'])['sales'].sum()`, pivot 'quarter' into column headers using `.unstack()`.

Accepted Answer

Optimal Solution:
import pandas as pd

grouped_series = df.groupby(['year', 'quarter'])['sales'].sum()

# unstack() moves the innermost index level to columns
pivoted = grouped_series.unstack(level=-1).reset_index()

Technical Explanation:
`.unstack()` pivots index levels into columns. `level=-1` targets the innermost index ('quarter').

year	Q1	Q2
2025	100	150
2026	120	NULL