select minimum value by ID, over range of visits

Question

I'm trying to extract a variable for the lowest value over a range of visits, in this case:

I want the lowest value over first 3 days of admission (admission day 1 or 2 or 3) , by VisitID. any suggestions?

visitID    value    day of admission
1          941       1
1          948       2
1          935       4

2           83       1
2           84       2
2           50       4
2           79       5

and I would want:

visitID  value   visit   minvalue

1        941      1       941
1        948      2       941
1        935      4       941

2        83       1        83
2        84       2        83
2        50       4        83
2        79       5        83

Answer 1

It would have been helpful if you had presented your data in an easily usable form. But here's an approach that should point you in a useful direction.

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte visitid int value byte day
1 941 1
1 948 2
1 935 4
2  83 1
2  84 2
2  50 4
2  79 5
end
bysort visitid (day) : egen minvalue = min(cond(day<=3,value,.))

Which results in

. list, sepby(visitid)

     +----------------------------------+
     | visitid   value   day   minvalue |
     |----------------------------------|
  1. |       1     941     1        941 |
  2. |       1     948     2        941 |
  3. |       1     935     4        941 |
     |----------------------------------|
  4. |       2      83     1         83 |
  5. |       2      84     2         83 |
  6. |       2      50     4         83 |
  7. |       2      79     5         83 |
     +----------------------------------+