ENH: new method Series.struct.assign to allow adding sub-fields to a struct

[tswast]

Feature Type

• Adding new functionality to pandas

• Changing existing functionality in pandas

• Removing existing functionality in pandas

Problem Description

When working with a Series with dtype pd.ArrowDtype(pa.struct(...)), it would be nice to have a way to add new sub-fields to the struct.

Feature Description

A new method assign on the StructAccessor with similar semantics as DataFrame.assign but instead of adding a new column to the DataFrame, it adds a new subfield to the struct and returns the struct Series.

This could use the pyarrow.compute.make_struct function to either add or replace the subfields in the existing struct array.

Alternative Solutions

__getitem__ and __setitem__ on StructAccessor could be a natural way to do this as well, but I'm not sure about adding inplace operations on an accessor object.

Additional Context

This would make struct (aka "record" / "nested") columns more useful for data read from BigQuery.