How to restart numbering of ID column from 0

[pramenon1066]

I have an ID column with IDs as such:

1900

1900

2345

2345

3209

3209

3209

4325

4325

4325

I would like to restart this numbering  from 0. For example, 1900 would be 0 and 2345 would be 1

0

0

1

1

2

2

2

3

3

3

Are there any formula's I can use to do this quickly?

[#2]

@pramenon1066 

=COUNT(UNIQUE($A$1:A1))-1

=BYROW(A1:A10,LAMBDA(row,COUNT(UNIQUE(A1:row))-1))

With Office 365 or Excel 2021 or Excel for the web you can try these formulas.

[#3]

@pramenon1066 

I think this was posted a week ago. Here's my take:

=LET(uArr,UNIQUE(arr),XMATCH(arr,uArr)-1)

[#4]

@pramenon1066 

If you work with an older version e.g. Excel 2013 you can use a helper formula which is in cell C2 in the example:

=IF(B2=B1,C1,C1+1)

And this is the formula in cell D2:

=C2-1

Both formulas can be filled down as required.