Generate variable based on previous value for other group variable

[Berit Alsson]

id	t	d	occur	t0	t_
1	0	0	0	-	-
1	1	0	0	-	-
1	2	1	1	0	2
1	3	1	2	2	3
1	4	0	2	-	-
1	5	0	2	-	-
1	6	1	3	3	6

Hi,

I'm trying to prepare my panel data for a survival analysis and now trying to generate the t0 variable indicating the starting time for the analysis.

t: time
d: status variable indicating whether individual been through event or not
occur: accumulated event
t0: analysis time when record begins
t_ : analysis time when record ends

So I'm trying to generate t0 variable: when id have experienced event (d=1), t0 is then suppose to obtain the minimum value of t in the previous group of occur
That is how I'm thinking of solving this problem but I cannot manage to solve it! and btw. I am going to delete the rows with the value - after generating all my variables.


(I have sensitive data so I cannot share an example)


Thanks!

[Andrew Musau]

This will give you what you want:

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(id t d occur) str1(t0 t_)
1 0 0 0 "-" "-"
1 1 0 0 "-" "-"
1 2 1 1 "0" "2"
1 3 1 2 "2" "3"
1 4 0 2 "-" "-"
1 5 0 2 "-" "-"
1 6 1 3 "3" "6"
end

bys  id (t): gen seq= 1+ sum(d>0)
bys seq: egen min_t= min(t)
bys  id (t): gen wanted= min_t[_n-1] if d

Res.:

. l, sep(0)

     +-----------------------------------------------------+
     | id   t   d   occur   t0   t_   seq   min_t   wanted |
     |-----------------------------------------------------|
  1. |  1   0   0       0    -    -     1       0        . |
  2. |  1   1   0       0    -    -     1       0        . |
  3. |  1   2   1       1    0    2     2       2        0 |
  4. |  1   3   1       2    2    3     3       3        2 |
  5. |  1   4   0       2    -    -     3       3        . |
  6. |  1   5   0       2    -    -     3       3        . |
  7. |  1   6   1       3    3    6     4       6        3 |
     +-----------------------------------------------------+

.

[Berit Alsson]

This will give you what you want:

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(id t d occur) str1(t0 t_)
1 0 0 0 "-" "-"
1 1 0 0 "-" "-"
1 2 1 1 "0" "2"
1 3 1 2 "2" "3"
1 4 0 2 "-" "-"
1 5 0 2 "-" "-"
1 6 1 3 "3" "6"
end

bys id (t): gen seq= 1+ sum(d>0)
bys seq: egen min_t= min(t)
bys id (t): gen wanted= min_t[_n-1] if d

Res.:

. l, sep(0)

+-----------------------------------------------------+
| id t d occur t0 t_ seq min_t wanted |
|-----------------------------------------------------|
1. | 1 0 0 0 - - 1 0 . |
2. | 1 1 0 0 - - 1 0 . |
3. | 1 2 1 1 0 2 2 2 0 |
4. | 1 3 1 2 2 3 3 3 2 |
5. | 1 4 0 2 - - 3 3 . |
6. | 1 5 0 2 - - 3 3 . |
7. | 1 6 1 3 3 6 4 6 3 |
+-----------------------------------------------------+

.

Thank you so much it worked wonderful !!