How to create a sequence within a group?

[Shanaz Sadique]

Hello,

I appreciate your help on this.

I have patient level data with and ID and subID. I want to generate the sequence (such as 1,2,3,4...) for the subID group within the ID.

e.g., this is how my data looks like

ID	SubID
A	x
A	x
A	y
A	y
B	m
B	m
B	n
B	n
B	o
B	o

I want the sequence to be generated as follows

ID	SubID	Sequence
A	x	1
A	x	1
A	y	2
A	y	2
B	m	1
B	m	1
B	n	2
B	n	2
B	o	3
B	o	3

appreciate your support very much

[Nick Cox]

Please follow https://www.statalist.org/forums/help#stata and use dataex to show examples.

* Example generated by -dataex-. For more info, type help dataex
clear
input str1(D SubId)
"A" "x"
"A" "x"
"A" "y"
"A" "y"
"B" "m"
"B" "m"
"B" "n"
"B" "n"
"B" "o"
"B" "o"
end

bysort D (SubId): gen wanted = sum(SubId != SubId[_n-1])

list , sepby(D SubId)

     +--------------------+
     | D   SubId   wanted |
     |--------------------|
  1. | A       x        1 |
  2. | A       x        1 |
     |--------------------|
  3. | A       y        2 |
  4. | A       y        2 |
     |--------------------|
  5. | B       m        1 |
  6. | B       m        1 |
     |--------------------|
  7. | B       n        2 |
  8. | B       n        2 |
     |--------------------|
  9. | B       o        3 |
 10. | B       o        3 |
     +--------------------+

[Shanaz Sadique]

Thank you Nick for the response, it worked