👀 Views: 456 💬 Answers: 1 📅 Created: 2025-06-05

pandas dataframe groupby aggregation Python

I need some guidance on I'm working with a `ValueError` when trying to apply a custom aggregation function using `groupby` on a DataFrame in Pandas 1.3.0... My goal is to group by a categorical column and then apply a custom function to sum up the values in another column, but instead, I'm getting this behavior: `ValueError: Must produce aggregated value`. Here's the structure of my DataFrame: ```python import pandas as pd data = { 'category': ['A', 'A', 'B', 'B', 'C'], 'values': [10, 20, 30, 40, 50], 'extra': [1, 2, 1, 2, 1] } df = pd.DataFrame(data) ``` I want to group by the `category` column and apply a custom aggregation that also takes `extra` into account. Here’s the custom function I wrote: ```python def custom_agg(group): return group['values'].sum() + group['extra'].sum() ``` When I try to run the following code: ```python result = df.groupby('category').agg(custom_agg) ``` I get the aforementioned `ValueError`. I’ve also tried using `apply` instead of `agg` like this: ```python result = df.groupby('category').apply(custom_agg) ``` But I still receive the same behavior. I've checked that the custom function returns a single value, and I'm not sure what I’m doing wrong. Any help on how to fix this scenario would be greatly appreciated! My development environment is Ubuntu. Am I missing something obvious? I've been using Python for about a year now. Any feedback is welcome!