Description
Pandas version checks
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I have checked that this issue has not already been reported.
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I have confirmed this bug exists on the latest version of pandas.
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I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
import pandas as pd
x = pd.DataFrame([[1, 2, 3], [3, 4, 5]], columns=["A", "A", "B"])
pd.melt(x, id_vars=["A"], value_vars=["B"])Issue Description
Error raised when melting on DataFrame with duplicate column headers
import pandas as pd
x = pd.DataFrame([[1, 2, 3], [3, 4, 5]], columns=["A", "A", "B"])
pd.melt(x, id_vars=["A"], value_vars=["B"])
Above raises:
File "pandas\core\reshape\melt.py", line 110, in melt
if not isinstance(id_data.dtype, np.dtype):
^^^^^^^^^^^^^
File "pandas\core\generic.py", line 6286, in __getattr__
return object.__getattribute__(self, name)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'DataFrame' object has no attribute 'dtype'. Did you mean: 'dtypes'?
From pandas\core\reshape\melt.py:108 pop method causes id_data to be assigned to a DataFrame object rather causing above AttributeError
for col in id_vars:
id_data = frame.pop(col)
if not isinstance(id_data.dtype, np.dtype):
When having duplicate column headers in a dataframe it raises an AttributeError, should this instead indicate a hint about melting on duplicated column headers? Possibly implement a check prior to .dtype being called?
Expected Behavior
Error raised should be indicative of duplicated column headers.
for col in id_vars:
id_data = frame.pop(col)
if isinstance(id_data, pd.DataFrame):
raise Exception(f"{col} is a duplicate column header")
if not isinstance(id_data.dtype, np.dtype):
Installed Versions
INSTALLED VERSIONS
commit : 0691c5c
python : 3.11.4
python-bits : 64
OS : Windows
OS-release : 10
Version : 10.0.19045
machine : AMD64
processor : Intel64 Family 6 Model 154 Stepping 3, GenuineIntel
byteorder : little
LC_ALL : None
LANG : None
LOCALE : English_United Kingdom.1252
pandas : 2.2.3
numpy : 1.26.4
pytz : 2024.2
dateutil : 2.9.0.post0
pip : 25.1.1
Cython : None
sphinx : None
IPython : None
adbc-driver-postgresql: None
adbc-driver-sqlite : None
bs4 : 4.13.4
blosc : None
bottleneck : None
dataframe-api-compat : None
fastparquet : None
fsspec : 2024.9.0
html5lib : None
hypothesis : None
gcsfs : None
jinja2 : 3.1.6
lxml.etree : 5.3.1
matplotlib : None
numba : None
numexpr : None
odfpy : None
openpyxl : 3.1.5
pandas_gbq : None
psycopg2 : None
pymysql : None
pyarrow : 17.0.0
pyreadstat : None
pytest : 8.3.3
python-calamine : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : 0.9.0
xarray : None
xlrd : 2.0.1
xlsxwriter : 3.2.0
zstandard : None
tzdata : 2024.2
qtpy : None
pyqt5 : None