How to manipulate only certain element belonging to an object list in Pandas DataFrame

Question

I have a pandas DataFrame in which several columns contain list of object like the following:

Index       A             B                  C
0       [1,2,3,]    [4,5,6,...20]      [1,2,3,...,64]
1       [1,2,3,]    [4,5,6,...20]      [1,2,3,...,64]
..
..
n       [1,2,3,]    [4,5,6,...20]      [1,2,3,...,64]

Of course numbers are just for reference. I would like to sum, let's say '10' to the first 32 values of the column 'C'. I tried to use apply fucntion with lambda in several ways without success. Could you help me? Thanks in advance!

Answer 1

It's not clear whether you want to:

• add 10 to all elements inside the lists in the first 32 rows of column C;
• add 10 to the first 32 elements of all lists of column C.

Both can be accomplished using apply with a lambda returning a list comprehension.

The former:

df.loc[0:32, 'C'] = df.loc[0:32, 'C'].apply(lambda lst: [x+10 for x in lst])

The latter:

df.C = df.C.apply(lambda lst: [x+10 if i < 32 else x for i, x in enumerate(lst)])