How to duplicate column values across the same id value python / pandas

Question

I want to know how can I duplicate the last not NaN value for column "count" for the same id instead of having NaN, for example :

df = pd.DataFrame({'id': [145, 145, 287,678, 678,678, 790, 790, 310, 310],
                       'date': [2021, 2022, 2022, 2020, 2021,2022, 2021, 2022, 2021, 2022],
                       'count': [10, np.nan, 35, 40, 40,np.nan, 60, np.nan, 17, np.nan]})

    In [10]: df
    Out[10]: 

         id     date    count
    0   145     2021    10.0
    1   145     2022    NaN
    2   287     2022    35.0
    3   678     2020    40.0
    4   678     2021    40.0
    5   678     2022    NaN
    6   790     2021    60.0
    7   790     2022    NaN
    8   310     2021    17.0
    9   310     2022    NaN

I want to get the following result :


    In [10]: df
    Out[10]: 
         id     date    count
    0   145     2021    10.0
    1   145     2022    10.0
    2   287     2022    35.0
    3   678     2020    40.0
    4   678     2021    40.0
    5   678     2022    40.0
    6   790     2021    60.0
    7   790     2022    60.0
    8   310     2021    17.0
    9   310     2022    17.0

score 2 · Accepted Answer · answered May 17 '22 at 10:24

2

print(df.fillna(method='ffill'))

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answered May 17 '22 at 10:24

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How to duplicate column values across the same id value python / pandas

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