1df2.replace(-999, np.nan, inplace=True)
2df2.fillna(df2.mean())
3
4 EventId A B C
50 100000 0.91 124.711 2.666000
61 100001 0.91 124.711 -0.202838
72 100002 0.91 124.711 -0.202838
83 100003 0.91 124.711 -0.202838