Scenario5

Source              
Col_1    Col_2       
D1       A1          
D1       A2          
D2       A3         
D2       A4           

D2       A5           

D3       A6           
D3       A7 

Target 
Col_1    Col_2   
D1     A1-A2 
D2    A3-A4-A5 
D3     A6-A7


Answer :

The Following can be obtained by using a Sorter transformation , Expression transformation and a aggregator transformation.

Let me show the mapping now.,

This shows the mapping for the above scenario.
Now lets see them in detail
1) Usual Sorter on Col1
2) Expression t/f like below

3) Aggregator t/f as below