Remove duplicates from one column and Concat data from another column

[Chalky1999]

Hi
I have an Excel sheet with multiple entries(see example). I need to remove the duplicates from columns 1&2 but keep the data in column 3. Ideally concatenating this data in to column 3 or a new column with all entries, separated by a dash. An example of output is attached.

There can be more than 2 duplicates of columns 1 & 2 within the sheet and a similar number of duplicates in column 3(to be retained)

Hope that makes sense but is it possible?

Thanks

[alansidman]

Here is a power query solution

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Excel 2016 (Windows) 64 bit

	A	B	C	D	E	F	G	H	I
1	column 1	column 2	column 3	Column 4		column 1	column 2	Custom	Column 4
2	abc1	abc2	1234	a		abc1	abc2	1234-5678	a
3	abc1	abc2	5678	g		bce2	bce3	4556	h
4	bce2	bce3	4556	h		def3	def4	5678	j
5	def3	def4	5678	j

Sheet: Sheet1