Answers for "df.fillna(method='mean')"

fillna with mean pandas

sub2['income'].fillna((sub2['income'].mean()), inplace=True)

df.fillna(-999,inplace=True)

df2.replace(-999, np.nan, inplace=True)
df2.fillna(df2.mean())

    EventId A       B        C
0   100000  0.91    124.711  2.666000
1   100001  0.91    124.711 -0.202838
2   100002  0.91    124.711 -0.202838
3   100003  0.91    124.711 -0.202838