How to Solve Complex Pandas Groupby Challenges with Simple Code

1. Introduction

Hello, I am Pipi. A few days ago, a member of a Python community asked a Pandas question, which I am sharing here.

Data sample:

2. Implementation Process

One contributor suggested using group sorting and concatenation, while another offered a different approach, as shown below:

Additional ideas included grouping by, resetting the index, and concatenating new columns; an Excel‑based method was also mentioned.

ChatGPT later provided a solution, the code is as follows:

df['编号'] = df.groupby(['日期', '凭证字号']).cumcount() + 1  # generate sequential number
df['凭证编号'] = df['日期'] + df['凭证字号'] + '-' + df['编号'].astype(str)

The problem was successfully resolved.

3. Summary

This article focused on a Python data‑processing challenge, offering detailed analysis and a working code example that helped the community address the issue effectively.

Thanks to the community members who contributed ideas and code.

Tip: When posting large datasets, consider anonymizing data and sharing a small demo file along with the relevant code and error screenshots. If the code is short, include it directly; for longer scripts, attach a .py file.