Use first function in Aggregaror Transformation .
Group by ColB
O_COLA : FIRST(COLA)
O_COLB : FIRST(COLB)
O_COLB : FIRST(COLC)
Then put an expression transformation and concat in a way you need.
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Using variables in expression and filter also this can be achived.
Source -> Sorter -> Expression -> Filter -> target
The best way would me to implement a mapping similar to the logic found in the mapping template for Aggregation Using Expression Transformation
You would need to modify it to do concatenation instead of aggregation. I've used this method with success in the past.
this has been resolved using java transformation.
Sandeep - Can you please put details how this has been resolved thru Jave trx