BUG: DataFrame.to_numpy() unnecessarily upcasts to object dtype.

[randolf-scholz]

Pandas version checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• I have confirmed this bug exists on the main branch of pandas.

Reproducible Example

import pandas as pd
df = pd.DataFrame({"a" : [1, 2], "b" : [3, 4]}, dtype="int64[pyarrow]")
assert df["a"].to_numpy().dtype == int  # ✅
assert df["b"].to_numpy().dtype == int  # ✅
assert df.to_numpy().dtype == int  # ❌ object dtype instead of int

Issue Description

All columns convert to int dtypes, but the full frame converts to object dtype.

Expected Behavior

One would expect a commutative property: the dtype of DataFrame.to_numpy() should be identical to the dtype of

np.stack([df[col].to_numpy() for col in df], axis=-1)

(In fact, this provides a naive way of implementing DataFrame.to_numpy().)

Installed Versions

INSTALLED VERSIONS

commit : d9cdd2e
python : 3.11.7.final.0
python-bits : 64
OS : Linux
OS-release : 6.5.0-41-generic
Version : #41~22.04.2-Ubuntu SMP PREEMPT_DYNAMIC Mon Jun 3 11:32:55 UTC 2
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 2.2.2
numpy : 2.0.0
pytz : 2024.1
dateutil : 2.9.0.post0
setuptools : 70.1.0
pip : 24.0
Cython : None
pytest : 8.2.2
hypothesis : 6.103.2
sphinx : 7.3.7
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.4
IPython : 8.25.0
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.3
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : 2024.6.0
gcsfs : None
matplotlib : 3.9.0
numba : None
numexpr : None
odfpy : None
openpyxl : 3.1.4
pandas_gbq : None
pyarrow : 16.1.0
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.13.1
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2024.1
qtpy : None
pyqt5 : None

[mroeschke]

Thanks for the report. The core issue is based in #22791 so will close in favor of that issue