Excel automatic numeration according to ID

Question

Given following table:

No.	ID
	HA
	PA
	PA
	PA
	HA
	PA
	HA
	PA
	PA
	HA

I would like to create a formula for the first column to create an automatic numbering where the main number always increments when ID="HA", and the secondary number always increments when ID="PA", like so:

No.	ID
1	HA
1.1	PA
1.2	PA
1.3	PA
2	HA
2.1	PA
3	HA
3.1	PA
3.2	PA
4	HA

If it helps, what I have got so far is:

=IF(B2="HA",COUNTIF($B$2:B2,"HA"),CONCAT(A1,".",COUNTIF(INDIRECT("B"&XMATCH("HA",$B$2:B2)),"PA")))

As you can see I am struggling with the second part, maybe someone can help me out from here.

Answer 1

With Microsoft-365 you may try SCAN() function.

=SCAN(0,B2:B11,LAMBDA(a,x,IF(x="HA",a+1,a)))+SCAN(0,B2:B11,LAMBDA(aa,xx,IF(xx="HA",0,aa+1)))/10

As per suggestion by @VBasic2008 in comment section, following formula is more simpler and elegant.

=SCAN(0,B2:B11,LAMBDA(a,x,IF(x="HA",INT(a)+1,a+0.1)))