Subgroup within id variable for panel data

[N Winters]

I have panel data with an id variable for each person, I want to generate a subgroup identifier based on consecutive number of days. Based on the dataex given at the end, I'd like to have a variable that gives:

id	drug	day	period
1	1	1	1
1	1	2	1
1	1	3	1
1	1	4	1
1	1	5	1
1	1	8	2
1	1	9	2
1	1	10	2
1	1	13	3
1	1	14	3

* Example generated by -dataex-. To install: ssc install dataex
clear
input int id byte drug float days
1 1 1
1 1 2
1 1 3
1 1 4
1 1 5
1 1 8
1 1 9
1 1 10
1 1 13
1 1 14
1 1 15
1 1 16
2 1 1
2 1 2
2 1 3
2 1 4
2 1 5
2 1 6
2 1 7
2 1 8
2 1 24
2 1 25
2 1 26
2 1 31
2 1 32
2 1 33
2 1 34
2 1 41
2 1 42
2 1 44
2 1 45
2 1 46
2 1 47
2 1 48
2 1 49
2 1 50
2 1 51
2 1 52
2 1 53
2 1 54
2 1 55
2 1 56
2 1 57
2 1 60
2 1 61
2 1 62
3 1 1
3 1 2
3 1 3
3 1 4
3 1 5
3 1 6
3 1 7
3 1 8
3 1 9
3 1 10
3 1 11
3 1 12
3 1 13
3 1 14
3 1 15
3 1 16
3 1 21
3 1 22
4 1 1
4 1 2
4 1 3
4 1 4
5 1 1
7 1 1
7 1 2
7 1 3
7 1 4
7 1 5
7 1 6
7 1 7
7 1 8
7 1 9
7 1 10
7 1 45
7 1 46
7 1 47
7 1 48
7 1 49
7 1 50
7 1 51
7 1 52
7 1 53
7 1 54
7 1 65
7 1 66
7 1 71
7 1 72
7 1 73
7 1 74
7 1 75
7 1 76
7 1 77
7 1 78
9 1 1
end

[Mike Lacy]

You have nice data examples here, but I don't understand the rules that map the data you have into what you want. In particular, the phrase "generate a subgroup identifier based on consecutive number of days" doesn't click for me; perhaps it does for someone else. "Consecutive number of days" for what? The "subgroup" would denote people who share what characteristic in common?
And, I don't know what "period" is supposed to designate: The period during which *what* prevails? I think it would increase your chances of a quick answer if you could explain this differently.

[William Lisowski]

I think what you are looking for is an indicator of "spells" of consecutive days - each time there's a break in the sequence, or a new id (I'm not sure of the role of drug) you want to start a new sequence.

There's a good discussion of this by Nick Cox in the Stata Journal paper (currently free to download) at https://www.stata-journal.com/articl...article=dm0079

Starting from your example data, the code below does what I understand you to want. It's left as an exercise for the reader to combine the two generate commands into one; I chose the wordier version to make it more apparent what is happening.

. by id (days), sort: generate newspell = days != days[_n-1]+1

. by id (days), sort: generate spell = sum(newspell)

. list, noobs sepby(id spell)

  +-------------------------------------+
  | id   drug   days   newspell   spell |
  |-------------------------------------|
  |  1      1      1          1       1 |
  |  1      1      2          0       1 |
  |  1      1      3          0       1 |
  |  1      1      4          0       1 |
  |  1      1      5          0       1 |
  |-------------------------------------|
  |  1      1      8          1       2 |
  |  1      1      9          0       2 |
  |  1      1     10          0       2 |
  |-------------------------------------|
  |  1      1     13          1       3 |
  |  1      1     14          0       3 |
  |  1      1     15          0       3 |
  |  1      1     16          0       3 |
  |-------------------------------------|
  |  2      1      1          1       1 |
  |  2      1      2          0       1 |
  |  2      1      3          0       1 |
  |  2      1      4          0       1 |
  |  2      1      5          0       1 |
  |  2      1      6          0       1 |
  |  2      1      7          0       1 |
  |  2      1      8          0       1 |
  |-------------------------------------|
  |  2      1     24          1       2 |
  |  2      1     25          0       2 |
  |  2      1     26          0       2 |
  |-------------------------------------|
  |  2      1     31          1       3 |
  |  2      1     32          0       3 |
  |  2      1     33          0       3 |
  |  2      1     34          0       3 |
  |-------------------------------------|
  |  2      1     41          1       4 |
  |  2      1     42          0       4 |
  |-------------------------------------|
  |  2      1     44          1       5 |
  |  2      1     45          0       5 |
  |  2      1     46          0       5 |
  |  2      1     47          0       5 |
  |  2      1     48          0       5 |
  |  2      1     49          0       5 |
  |  2      1     50          0       5 |
  |  2      1     51          0       5 |
  |  2      1     52          0       5 |
  |  2      1     53          0       5 |
  |  2      1     54          0       5 |
  |  2      1     55          0       5 |
  |  2      1     56          0       5 |
  |  2      1     57          0       5 |
  |-------------------------------------|
  |  2      1     60          1       6 |
  |  2      1     61          0       6 |
  |  2      1     62          0       6 |
  |-------------------------------------|
  |  3      1      1          1       1 |
  |  3      1      2          0       1 |
  |  3      1      3          0       1 |
  |  3      1      4          0       1 |
  |  3      1      5          0       1 |
  |  3      1      6          0       1 |
  |  3      1      7          0       1 |
  |  3      1      8          0       1 |
  |  3      1      9          0       1 |
  |  3      1     10          0       1 |
  |  3      1     11          0       1 |
  |  3      1     12          0       1 |
  |  3      1     13          0       1 |
  |  3      1     14          0       1 |
  |  3      1     15          0       1 |
  |  3      1     16          0       1 |
  |-------------------------------------|
  |  3      1     21          1       2 |
  |  3      1     22          0       2 |
  |-------------------------------------|
  |  4      1      1          1       1 |
  |  4      1      2          0       1 |
  |  4      1      3          0       1 |
  |  4      1      4          0       1 |
  |-------------------------------------|
  |  5      1      1          1       1 |
  |-------------------------------------|
  |  7      1      1          1       1 |
  |  7      1      2          0       1 |
  |  7      1      3          0       1 |
  |  7      1      4          0       1 |
  |  7      1      5          0       1 |
  |  7      1      6          0       1 |
  |  7      1      7          0       1 |
  |  7      1      8          0       1 |
  |  7      1      9          0       1 |
  |  7      1     10          0       1 |
  |-------------------------------------|
  |  7      1     45          1       2 |
  |  7      1     46          0       2 |
  |  7      1     47          0       2 |
  |  7      1     48          0       2 |
  |  7      1     49          0       2 |
  |  7      1     50          0       2 |
  |  7      1     51          0       2 |
  |  7      1     52          0       2 |
  |  7      1     53          0       2 |
  |  7      1     54          0       2 |
  |-------------------------------------|
  |  7      1     65          1       3 |
  |  7      1     66          0       3 |
  |-------------------------------------|
  |  7      1     71          1       4 |
  |  7      1     72          0       4 |
  |  7      1     73          0       4 |
  |  7      1     74          0       4 |
  |  7      1     75          0       4 |
  |  7      1     76          0       4 |
  |  7      1     77          0       4 |
  |  7      1     78          0       4 |
  |-------------------------------------|
  |  9      1      1          1       1 |
  +-------------------------------------+

[N Winters]

I think what you are looking for is an indicator of "spells" of consecutive days - each time there's a break in the sequence, or a new id (I'm not sure of the role of drug) you want to start a new sequence.

There's a good discussion of this by Nick Cox in the Stata Journal paper (currently free to download) at https://www.stata-journal.com/articl...article=dm0079

Starting from your example data, the code below does what I understand you to want. It's left as an exercise for the reader to combine the two generate commands into one; I chose the wordier version to make it more apparent what is happening.
[CODE]
. by id (days), sort: generate newspell = days != days[_n-1]+1

. by id (days), sort: generate spell = sum(newspell)

Thanks William, this is what I am looking for. I will also take a look at Nick's discussion.