Context changes to a counter variable

SDN gurus,

any thoughts on how to go for this..

Input Structure

Node A

NodeB

NodeB

NodeB

Node A

Node B

Target

Node A

Node B

1

Node B

2

Node B

3

Node A

Node B

1

Has to be a udf, as the standard function ...counter..doesent support context changes.......thoughts on this ..?

Regards

Ravi Raman