BUG: Stack creates duplicate column

[soerenwolfers]

import numpy as np
import pandas as pd

df = pd.DataFrame(
    np.zeros([1, 5]), 
    columns=pd.MultiIndex.from_tuples(
        [
            (0, None, None), 
            (0, 0, 0),
            (0, 0, 1),
            (0, 1, 0),
            (0, 1, 1),
        ],
    )
)

df.stack(2)

INSTALLED VERSIONS
------------------
commit           : b5958ee1999e9aead1938c0bba2b674378807b3d
python           : 3.6.6.final.0
pandas           : 1.1.5
numpy            : 1.17.4

[phofl]

That is not really a duplicate, the first 1 is representing the NaN. The MultiIndex handling was not correct.

[soerenwolfers]

Right, my original problem was that I got an error when trying to stack both the last two levels of the columns. Error message said something about duplicate columns, and when I made the MWE it seemed to fit

[aelshazlyIT]

might be the MultiIndex handling was not correct.

[phofl]

That is not really a duplicate, the first 1 is representing the NaN. The MultiIndex handling was not correct.

Yes, is fixed in my pr