Some interesting behavior from .groupby().apply( .to_records() )

Why is it that

df.groupby('A')[['B','C']].apply(lambda x: x.to_records())

throws: TypeError: Series.name must be a hashable type while

df.groupby('A').apply(lambda x: x[['B','C']].to_records())

works?

[bobhaffner]

I had some time this morning so I looked at this. Here’s what I found out.

This looks like the line where things head south. https://github.com/pandas-dev/pandas/blob/ee9c7e9b19a1fa3c4499d10885dec72f1d651832/pandas/core/series.py#L248

The successful line below has name = None df.groupby('A').apply(lambda x: x[['B','C']].to_records()) # => Succeeds

and the line that errors has a name = [‘B’, ‘C’]
df.groupby('A')[['B','C']].apply(lambda x: x.to_records()) # => TypeError

ps. swapping out to_records for something similar like to_dict does work df.groupby('A')['B','C'].apply(lambda x: x.to_dict())

[javiqm12]

Having same issue here 😦 with pandas 1.3.5