Replace pandas zero value with ffill non-zero, if the subsequent value is non-zero

Question

I need to replace "0" row data in pandas with the previous rows non-zero value IF and ONLY IF, the value in the row following the "0" is non zero.

I.e.

101
92
78
0
107
0
0

would become:

101
92
78
78
107
0
0

Any ideas how to do this would be much appreciated :-)

Thanks!

Answer 1

using shift you could do

In [608]: df.loc[(df.val == 0) & (df.val.shift(-1) != 0), 'val'] = df.val.shift(1)

In [609]: df
Out[609]:
     val
0  101.0
1   92.0
2   78.0
3   78.0
4  107.0
5    0.0
6    0.0