BUG: Shift on DataFrame which has more than 1 block creates wrong result · Issue #35488 · pandas-dev/pandas (original) (raw)

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Code Sample, a copy-pastable example

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In [1]: import pandas as pd

In [2]: import numpy as np

In [3]: df1 = pd.DataFrame(np.random.randint(1000, size=(5, 3)))

In [4]: df2 = pd.DataFrame(np.random.randint(1000, size=(5, 2)))

In [5]: df3 = pd.concat([df1, df2], axis=1)

In [6]: df3
Out[6]: 0 1 2 0 1 0 61 536 154 766 179 1 484 18 15 787 766 2 391 171 715 836 654 3 914 969 765 824 950 4 169 414 759 16 666

In [7]: len(df3._data.blocks)
Out[7]: 2

In [9]: df3.shift(2, axis=1)
Out[9]: 0 1 2 0 1 0 NaN NaN 61.0 NaN NaN 1 NaN NaN 484.0 NaN NaN 2 NaN NaN 391.0 NaN NaN 3 NaN NaN 914.0 NaN NaN 4 NaN NaN 169.0 NaN NaN

Problem description

[this should explain why the current behaviour is a problem and why the expected output is a better solution]

I guess shift is applied to both of the internal blocks.

Expected Output

I forced consolidate, the result is right.

In [12]: df3._data._consolidate_inplace()                                       

In [13]: df3.shift(2, axis=1)                                                   
Out[13]: 
    0   1      2      0      1
0 NaN NaN   61.0  536.0  154.0
1 NaN NaN  484.0   18.0   15.0
2 NaN NaN  391.0  171.0  715.0
3 NaN NaN  914.0  969.0  765.0
4 NaN NaN  169.0  414.0  759.0

Output of pd.show_versions()

In [14]: pd.show_versions()

/Users/qinxuye/miniconda3/envs/test_pandas_1.1/lib/python3.7/site-packages/setuptools/distutils_patch.py:26: UserWarning: Distutils was imported before Setuptools. This usage is discouraged and may exhibit undesirable behaviors or errors. Please use Setuptools' objects directly or at least import Setuptools first.
"Distutils was imported before Setuptools. This usage is discouraged "

ImportError Traceback (most recent call last)
in
----> 1 pd.show_versions()

~/miniconda3/envs/test_pandas_1.1/lib/python3.7/site-packages/pandas/util/_print_versions.py in show_versions(as_json)
104 """
105 sys_info = _get_sys_info()
--> 106 deps = _get_dependency_info()
107
108 if as_json:

~/miniconda3/envs/test_pandas_1.1/lib/python3.7/site-packages/pandas/util/_print_versions.py in _get_dependency_info()
82 for modname in deps:
83 mod = import_optional_dependency(
---> 84 modname, raise_on_missing=False, on_version="ignore"
85 )
86 result[modname] = _get_version(mod) if mod else None

~/miniconda3/envs/test_pandas_1.1/lib/python3.7/site-packages/pandas/compat/_optional.py in import_optional_dependency(name, extra, raise_on_missing, on_version)
97 minimum_version = VERSIONS.get(name)
98 if minimum_version:
---> 99 version = _get_version(module)
100 if distutils.version.LooseVersion(version) < minimum_version:
101 assert on_version in {"warn", "raise", "ignore"}

~/miniconda3/envs/test_pandas_1.1/lib/python3.7/site-packages/pandas/compat/_optional.py in _get_version(module)
42
43 if version is None:
---> 44 raise ImportError(f"Can't determine version for {module.name}")
45 return version
46

ImportError: Can't determine version for numba