Index duplicates then order by alphabetical order

[Anonymous]

I created a table using the 'earlier' dax function, but I am now having problems dealing with the duplicates.

The tables below would illustrate.

Activity ID		Department		Date		Count
1203993		Young		15-03-2021		20
1394994		Young		15-03-2021		20
1475478		Young		15-03-2021		20
1458990		Young		15-03-2021		20
1457373		Young		16-03-2021		16
1243536		Young		16-03-2021		16
5647747		Ran		13-03-2021		14
5657757		Ran		13-03-2021		14
7907000		Ran		15-03-2021		12
5768688		Ran		15-03-2021		12
5767678		Ran		15-03-2021		12

I am thinking the way to do this would be to create a new index column that gives unique indexes based on filtering criteria as below:

Activity ID		Department		Date		Count		Index
1203993		Young		15-03-2021		20		1
1394994		Young		15-03-2021		20		2
1475478		Young		15-03-2021		20		3
1458990		Young		15-03-2021		20		4
1457373		Young		16-03-2021		16		1
1243536		Young		16-03-2021		16		2
5647747		Ran		13-03-2021		14		1
5657757		Ran		13-03-2021		14		2
7907000		Ran		15-03-2021		12		1
5768688		Ran		15-03-2021		12		2
5767678		Ran		15-03-2021		12		3

The index would be based on the Activity ID (which are string elements). So invariably, the table is filtered for Department and Dates then an index is generated based on the alphabetical ordering of the Activity ID. I can then filter out the duplicates by selecting the Index 1 as below.

Activity ID		Department		Date		Count		Index
1203993		Young		15-03-2021		20		1
1457373		Young		16-03-2021		16		1
5647747		Ran		13-03-2021		14		1
7907000		Ran		15-03-2021		12		1

I have tried using rank and calculate, but  generated error. I would appreciate if someone can advice what to do...or maybe an easier way to deal with duplicates after using the earlier function.