I have lot of data in this format. A,B & C are column and 1,2,3 are rows
A B C
1 a 35
2 b
3 p
4 c 45
5 d 55
6 e 45
7 f 55
8 g 45
there are no simetrycally data.

I want to add b for rows 2 to a for rows 1 like that
A B C
1 ab 35
2
3 cd 45
4 55
5 ef 45
6 55
7 g 45
Pl help me that how can do this thing in short cut method.