逐列填充模式

Question

I got some like this: x: Users y: Ratings

and this shows user 1 rating movie 1 with 4.0 user 1 not rating movie 2 user 1 rating movie 3 with 1.0 and so

       rating
movieId 1      2      3      4     5   .....
userID
1      4.0    NaN     1.0   4.1    NaN
2      NaN      2     5.1   NaN    NaN
3      3.0    2.0     NaN   NaN    NaN
4      5.0    NaN     2.8   NaN    NaN

How could I fill NaN values with mode by Movie

example movieId 1 has ratings 4.0, NaN, 3.0, 5.0..... then fill NaNs with 4.0(mode) i tried to use fillna

rating.apply(lambda x: x.fillna(x.mode().item()))

Answer 1

Try

rating.apply(lambda x: x.fillna(x.mode()), axis=0)

specify axis=0

Alternatively,

import numpy as np
import pandas as pd

def fillna_mode(df, cols_to_fill):
    for col in cols_to_fill:
        df[col].fillna(df[col].mode()[0], inplace=True)

sample = {1: [4.0, np.nan,1.0, 4.1, np.nan],
          2: [np.nan, 2, 5.1, np.nan, np.nan]}

rating = pd.DataFrame(sample)

print(rating)

      1 2
0   4.0 NaN
1   NaN 2.0
2   1.0 5.1
3   4.1 NaN
4   NaN NaN

fillna_mode(rating, [1, 2])

Output

    1   2
0   4.0 2.0
1   1.0 2.0
2   1.0 5.1
3   4.1 2.0
4   1.0 2.0