扩大熊猫行中的平均值

Question

I am trying to calculate expanding mean on rows in my dataframe using pandas. All seems to be working fine if calculating for columns:

>>> t = pd.DataFrame([1,2,3,4,5,np.nan])

>>> t
     0
0  1.0
1  2.0
2  3.0
3  4.0
4  5.0
5  NaN

>>> t.expanding(min_periods=2, axis=0).mean()
     0
0  NaN
1  1.5
2  2.0
3  2.5
4  3.0
5  3.0

however if I try the same rows, I get wrong results (seems like window of size 2 is applied all the time):

>>> t.T
     0    1    2    3    4   5
0  1.0  2.0  3.0  4.0  5.0 NaN

>>> t.T.expanding(min_periods=2, axis=1).mean()
    0    1    2    3    4   5
0 NaN  1.5  2.5  3.5  4.5 NaN

seems like bug to me, but maybe I'm missing something... any clues please?

Answer 1

It is indeed a bug, listed on github-pandas-expanding and github-pandas-rolling .

Thanks.