Return unique values from one column and Concatenate corresponding values from another

With Power Pivot.
1. Highlight your source data.
2. Click on I nsert
3. Select Pivot Table
4. Make sure to select the box "Add to Data Model"
5. Select where you want your output
6. In the Pivot Table Fields, put "Letters " in the Rows
7. Right click on the Range and select Add a measure
8. Give the measure a name.
9. In the forumula area type:=CONCATENATEX(Range,Range[Numbers],", ")
10. Select your newly named measure and drag it to the Values

Excel 2016 (Windows) 32 bit

	A	B
3	Letters	NewNum
4	ABC	4, 2, 5
5	CDE	2
6	DWW	7, 9

Sheet: Sheet2