BUG: rounding dates to 30mins does not work

[Andre-Medina]

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

dates = pd.Series([pd.to_datetime("2022-01-11 12:10:00")])

# date should be rounded but is not
dates.round("30min")
# >0   2022-01-11 12:10:00
# >dtype: datetime64[ns]

# Round just date works
dates[0].round("30min")
# >Timestamp('2022-01-11 12:00:00')

Issue Description

Issue with the latest version of pandas (2.2.0). Rounding dates at 30 min increments does not round dates if they are in a series. This was working in pandas (2.1.4)

Expected Behavior

Dates should be rounded to 30 minute increments

import pandas as pd

dates = pd.Series([pd.to_datetime("2022-01-11 12:10:00")])

# Round just date works
dates[0].round("30min")

Installed Versions

INSTALLED VERSIONS

commit : 53525ea
python : 3.10.0.final.0
python-bits : 64
OS : Linux
OS-release : 5.15.133.1-microsoft-standard-WSL2
Version : #1 SMP Thu Oct 5 21:02:42 UTC 2023
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 3.0.0.dev0+152.g53525ea1c3
numpy : 1.26.2
pytz : 2023.3.post1
dateutil : 2.8.2
setuptools : 68.2.2
pip : 23.3.1
Cython : None
pytest : 7.4.3
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : 3.1.9
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.18.1
pandas_datareader : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.2
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : 2023.12.2
gcsfs : 2023.12.2post1
matplotlib : 3.8.2
numba : 0.58.1
numexpr : None
odfpy : None
openpyxl : 3.1.2
pandas_gbq : None
pyarrow : 14.0.1
pyreadstat : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : 1.11.4
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
zstandard : None
tzdata : 2023.3
qtpy : None
pyqt5 : None

[MarcoGorelli]

thanks @Andre-Medina for the report, this needs fixing, running a git bisect now

[MarcoGorelli]

From git bisect, this was introduced in #56767, @phofl

[phofl]

I am not sure that it is sensible to fix this, the new behavior aligns with DataFrame, which didn't support this before either.

dates.dt.round("30min")

That's what you want to do, we can fix this theoretically, but we should address the dataframe behavior as well then

[valeriupredoi]

hello 🐼 folks, you guys gonna fix this in 2.2.3 please? Cheers muchly 🍺

[Andre-Medina]

re-raised this issue as it is still broken.