Data interchange

[Ratmadeep]

f1 f2
a b
a b
a c
a c
a c

Final output

f1 f2 f3
a b c
a b c
a c b
a c b
a c b

[Lisa_P]

What is the logic to follow ?

[Ratmadeep]

there alaways two distinct value(b,c) in f2. in the final column in places of all b value there will be c value and vise versa.