Given two pandas DataFrames, df_employee and df_department, write code to join them on the employee ID, select the default columns, and write the resulting DataFrame back to a file.

Question

Assisting AI · Accepted Answer

```python
import pandas as pd
# Assume df_employee and df_department are already loaded
# Join on employee_id
result = pd.merge(df_employee, df_department, on='employee_id', how='inner')
# Write to CSV
result.to_csv('employee_department.csv', index=False)
```
This performs an inner join in O(n+m) time, where n and m are the row counts of the two DataFrames.

Given two pandas DataFrames, df_employee and df_department, write code to join them on the employee ID, select the default columns, and write the resulting DataFrame back to a file.

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