python dataframe, groupby based on one column and fill null values from another column using last non-null value

Question

I have a dataframe that has values for names based on multiple dates. I have created a series of null values for each name on a new date, and want to fill null values of one column based on the last non-null value for that name.

data = {'name':  ['Alex', 'Ben', 'Marry','Alex', 'Ben', 'Marry'],
        'job': ['teacher', 'doctor', 'engineer','teacher', 'doctor', 'engineer'],
        'age': ['27', '32', '78','27', '32', '78'],
        'weight': ['160', '209', '130','164', '206', '132'],
        'date': ['6-12-2022', '6-12-2022', '6-12-2022','6-13-2022', '6-13-2022', '6-13-2022']
        }

df = pd.DataFrame(data)
df

After adding null values:

    |name   |job        |age|weight |date
|---|-------|-----------|---|-------|--------
|0  |Alex   |teacher    |27 |160    |6-12-2022
|1  |Ben    |doctor     |32 |209    |6-12-2022
|2  |Marry  |engineer   |78 |130    |6-12-2022
|3  |Alex   |teacher    |27 |164    |6-13-2022
|4  |Ben    |doctor     |32 |206    |6-13-2022
|5  |Marry  |engineer   |78 |132    |6-13-2022
|6  |Alex   |NaN        |NaN|NaN    |6-14-2022
|7  |Ben    |NaN        |NaN|NaN    |6-14-2022
|8  |Marry  |NaN        |NaN|NaN    |6-14-2022

Now I need to fill null values for job, and age based on last entered value for that name.

Appreciate your help

Thanks

Answer 1

If I understand you correctly, you can .groupby() and then .ffill() :

df[["job", "age", "weight"]] = df.groupby("name")[["job", "age", "weight"]].ffill()

print(df)

Prints:

    name       job   age  weight       date
0   Alex   teacher  27.0   160.0  6-12-2022
1    Ben    doctor  32.0   209.0  6-12-2022
2  Marry  engineer  78.0   130.0  6-12-2022
3   Alex   teacher  27.0   164.0  6-13-2022
4    Ben    doctor  32.0   206.0  6-13-2022
5  Marry  engineer  78.0   132.0  6-13-2022
6   Alex   teacher  27.0   164.0  6-14-2022
7    Ben    doctor  32.0   206.0  6-14-2022
8  Marry  engineer  78.0   132.0  6-14-2022