BUG: Merge_asof fails for unknow reason #62497
Description
Pandas version checks
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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
from io import StringIO
alloc_txt = """User_Id Date Allocated_Points alloc_flag_day
1 466 2025-02-08 560 True
1 469 2025-02-08 560 True"""
red_txt = """User_Id Date Deducted_Points red_flag_day
1 466 2025-02-08 560 True
2 728 2025-02-02 750 True
3 728 2025-02-09 540 True
4 829 2025-04-03 800 True
5 869 2025-04-22 1400 True"""
# Read as if reading a CSV/TSV file
alloc_df = pd.read_csv(StringIO(alloc_txt), delim_whitespace=True)
red_df = pd.read_csv(StringIO(red_txt), delim_whitespace=True)
alloc_df['User_Id'] = alloc_df['User_Id'].astype(int)
red_df['User_Id'] = red_df['User_Id'].astype(int)
# Ensure date is datetime and remove any possible NaT
alloc_df = alloc_df[alloc_df['Date'].notnull()]
red_df = red_df[red_df['Date'].notnull()]
alloc_df['Date'] = pd.to_datetime(alloc_df['Date'])
red_df['Date'] = pd.to_datetime(red_df['Date'])
try:
one_result = pd.merge_asof(
alloc_df,
red_df,
by='User_Id',
left_on='Date',
right_on='Date',
direction='forward',
tolerance=pd.Timedelta(days=3),
suffixes=('_alloc', '_red')
)
print("Success!", one_result)
except Exception as ex:
print("Fails for first row alone:", ex)Issue Description
I am trying to find the users who have redeemed some points within 3 days of allocation. This is a sample data.
Not sure why this fails.
Expected Behavior
Ideally it should return the users who have entries in red_df within 3 days of alloc_df
Installed Versions
INSTALLED VERSIONS
commit : 4665c10
python : 3.12.9
python-bits : 64
OS : Linux
OS-release : 5.15.167.4-microsoft-standard-WSL2
Version : #1 SMP Tue Nov 5 00:21:55 UTC 2024
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : C.UTF-8
pandas : 2.3.2
numpy : 2.2.5
pytz : 2025.2
dateutil : 2.9.0.post0
pip : 25.0
Cython : None
sphinx : None
IPython : 8.30.0
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.12.3
blosc : None
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : None
html5lib : None
hypothesis : None
gcsfs : None
jinja2 : 3.1.6
lxml.etree : None
matplotlib : 3.10.3
numba : None
numexpr : None
odfpy : None
openpyxl : 3.1.5
pandas_gbq : None
psycopg2 : None
pymysql : None
pyarrow : None
pyreadstat : None
pytest : None
python-calamine : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : 2.0.40
tables : None
tabulate : 0.9.0
xarray : None
xlrd : None
xlsxwriter : None
zstandard : 0.23.0
tzdata : 2025.2
qtpy : 2.4.1
pyqt5 : None