Filling 0 with previous value at index

I have a df:

           1    2   3   4   5   6   7   8   9   10

A          10   0   0   15  0   21  45  0   0   7

I am trying fill index A values with the current value if the next value is 0 so that the df would look like this:

           1    2   3   4   5   6   7   8   9   10

A          10   10  10  15  15  21  45  45  45   7

I tried:

df.loc[['A']].replace(to_replace=0, method='ffill').values

But this does not work, where is my mistake?

>Solution :

If you want to use your method, you need to work with Series on both sides:

df.loc['A'] = df.loc['A'].replace(to_replace=0, method='ffill')

Alternatively, you can mask the 0 with NaNs, and ffill the data on axis=1:

df.mask(df.eq(0)).ffill(axis=1)

output:

      1     2     3     4     5     6     7     8     9   10
A  10.0  10.0  10.0  15.0  15.0  21.0  45.0  45.0  45.0  7.0