Increment Number By Value With Condition - Array Formula

Question

i'm confused with the following condition, simply i want to have arrayformula or maybe a custom-formula to increment number in a way bound by specific condition based on value in other column, put it simply :

if the group doesn't change and sub-group is different increment number by 1
else if the group doesn't change and sub-group is doesn't change (same) hold value by previous
else if the group change regardless sub-group value reset number back to 1

for ilustration

** notes Number is the result that i want, in example i fill it manually

Group	Sub-Group	Animal	Number
Land	poisonus	snake	1
land	friendly	dog	2
land	friendly	cat	2
land	scary	lion	3
aquatic	friendly	nemo fish	1
aquatic	predator	shark	2

UPDATE (dummy file link) :
https://docs.google.com/spreadsheets/d/1DAPf-DvWz50_DJ0IqAoSHbfEnfg_mN1lNXHcCjkj27M/edit#gid=0

Answer 1

try:

=INDEX(IF(A4:A="",,VLOOKUP(A4:A&B4:B, {UNIQUE(A4:A&B4:B), COUNTIFS(
 REGEXEXTRACT(UNIQUE(A4:A&"×"&B4:B), "(.*)×"), 
 REGEXEXTRACT(UNIQUE(A4:A&"×"&B4:B), "(.*)×"), 
 SEQUENCE(COUNTA(UNIQUE(A4:A&"×"&B4:B))), "<="&
 SEQUENCE(COUNTA(UNIQUE(A4:A&"×"&B4:B))))}, 2, 0)))