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pythonpandasdataframefillna

Forward Fill NA

I have a table with NaN.

import pandas as pd

data = {'name': ['may','may', 'mary', 'james','james','john','paul', 'paul', 'joseph'],
       'email' : ['may@gmail.com','NaN','Mary@gmail.com','James@gmail.com','NaN','NaN','Paul@gmail.com','NaN','NaN']}

df = pd.DataFrame(data)

BEFORE

enter image description here

DESIRE OUTPUT

enter image description here

But, when I use ffill, I ended up with this which is incorrect. Is there a way I can use ffill but with conditions?

enter image description here

Solution

  • In your example, NaN values are strings, with value "NaN". So before you fillna, you'd have to convert those to actual null values.

    import pandas as pd
import numpy as np

data = {'name': ['may','may', 'mary', 'james','james','john','paul', 'paul', 'joseph'],
       'email' : ['may@gmail.com','NaN','Mary@gmail.com','James@gmail.com','NaN','NaN','Paul@gmail.com','NaN','NaN']}

df = pd.DataFrame(data)

df['email'] = df['email'].replace({'NaN':np.nan})
df['email'] = df.groupby('name')['email'].fillna(method='ffill')
df

         name            email
0     may    may@gmail.com
1     may    may@gmail.com
2    mary   Mary@gmail.com
3   james  James@gmail.com
4   james  James@gmail.com
5    john              NaN
6    paul   Paul@gmail.com
7    paul   Paul@gmail.com
8  joseph              NaN