Replace values for all rows of a study ID, based on a value in a single row.

[Nate Fitzpatrick]

Hello, I am very new to stata and trying to teach myself how to use it. I wanted to determine if there is a way to generate a new variable, or replace an existing variable for all rows relevant to a specific patient ID, based on an observation from a single row.

ID	var1	visit	newvar
1	0	1	0
1	0	2	0
1	0	3	0
1	1	4	0
1	0	5	0
2	0	1	0
2	1	2	0
2	0	3	0
2	0	4	0

So if the observation for Study ID #1 in visit 5 is 1, how can I replace the value for newvar in all rows for patient #1 if var1==1 at visit 5.

Hopefully this makes sense.
Thank you so much.

[Carlo Lazzaro]

Nate:
the following toy-example considers that -1- for -var1-, -ID1- is reported at -visit- #4 (not #5):

. bysort ID (visit): replace newvar=1 if var1[4]==1


. list

     +----------------------------+
     | ID   var1   visit   newvar |
     |----------------------------|
  1. |  1      0       1        1 |
  2. |  1      0       2        1 |
  3. |  1      0       3        1 |
  4. |  1      1       4        1 |
  5. |  1      0       5        1 |
     |----------------------------|
  6. |  2      0       1        0 |
  7. |  2      1       2        0 |
  8. |  2      0       3        0 |
  9. |  2      0       4        0 |
     +----------------------------+

.

[William Lisowski]

Perhaps this is what you want. Note that for clarity I changed the observation of var1 for id 2 at visit 2 to 7. This assumes that var1 is 0 except for one observation when it has a positive value.

. * Example generated by -dataex-. For more info, type help dataex
. clear

. input int(id var1 visit)

           id      var1     visit
  1. 1 0 1
  2. 1 0 2
  3. 1 0 3
  4. 1 1 4
  5. 1 0 5
  6. 2 0 1
  7. 2 7 2
  8. 2 0 3
  9. 2 0 4
 10. end

. 
. bysort id (visit): egen newvar = max(var1)

. list, sepby(id)

     +----------------------------+
     | id   var1   visit   newvar |
     |----------------------------|
  1. |  1      0       1        1 |
  2. |  1      0       2        1 |
  3. |  1      0       3        1 |
  4. |  1      1       4        1 |
  5. |  1      0       5        1 |
     |----------------------------|
  6. |  2      0       1        7 |
  7. |  2      7       2        7 |
  8. |  2      0       3        7 |
  9. |  2      0       4        7 |
     +----------------------------+

.