Grouping of subset of a Column in pandas

August 4, 2022

Having a data set as below.Here I need to group the subset in column and fill the missing values using mode method.

Need to group the value ‘Tom’ from name and fill the missing value in value using mode.

     Name  Value
0     Tom   20.0
1     Tom   20.0
2     Tom    NaN
3    nick   19.0
4    nick   18.0
5   krish   15.0
6    nick   15.0
7    nick   20.0
8    jack    NaN
9     Tom   23.0
10    Tom    NaN

I tried the code below:

data['value']= data.loc[data["Name"]=='Tom'].fillna(data['value'].mode()[0], inplace=True)

Didn’t get the output as expected.

>Solution :

To replace on specific conditions you could use np.where() to evaluate the condition, when it is met, replace it with the mode, otherwise retain the column’s original value. Kindly try:

data['Value'] = np.where(data['Name'] =='Tom',data['Value'].fillna(data['Value'].mode()[0]),data['Value'])

This returns:

     Name  Value
0     Tom   20.0
1     Tom   20.0
2     Tom   20.0
3    nick   19.0
4    nick   18.0
5   krish   15.0
6    nick   15.0
7    nick   20.0
8    jack    NaN
9     Tom   23.0
10    Tom   20.0