Assigning dates and days of week in a long dataset

[Sarah Haynes]

Hello,

I have a long dataset with observations that represent all of the days that a person was enrolled in a study (day1, day2, day3, etc). For day 1 for each person, I have an actual calendar date ("date"). I would like fill in the rest of the date variable with calendar dates based on this first day (so day2=(date+1), day3= (date+2), etc).

Below is a dataex example including person ID number (idn), day (1-100) and date.

Thank you very much for your help,

Sarah

* Example generated by -dataex-. To install: ssc install dataex
clear
input int(idn day) float date
1   1 18919
1   2     .
1   3     .
1   4     .
1   5     .
1   6     .
1   7     .
1   8     .
1   9     .
1  10     .
1  11     .
1  12     .
1  13     .
1  14     .
1  15     .
1  16     .
1  17     .
1  18     .
1  19     .
1  20     .
1  21     .
1  22     .
1  23     .
1  24     .
1  25     .
1  26     .
1  27     .
1  28     .
1  29     .
1  30     .
1  31     .
1  32     .
1  33     .
1  34     .
1  35     .
1  36     .
1  37     .
1  38     .
1  39     .
1  40     .
1  41     .
1  42     .
1  43     .
1  44     .
1  45     .
1  46     .
1  47     .
1  48     .
1  49     .
1  50     .
1  51     .
1  52     .
1  53     .
1  54     .
1  55     .
1  56     .
1  57     .
1  58     .
1  59     .
1  60     .
1  61     .
1  62     .
1  63     .
1  64     .
1  65     .
1  66     .
1  67     .
1  68     .
1  69     .
1  70     .
1  71     .
1  72     .
1  73     .
1  74     .
1  75     .
1  76     .
1  77     .
1  78     .
1  79     .
1  80     .
1  81     .
1  82     .
1  83     .
1  84     .
1  85     .
1  86     .
1  87     .
1  88     .
1  89     .
1  90     .
1  91     .
1  92     .
1  93     .
1  94     .
1  95     .
1  96     .
1  97     .
1  98     .
1  99     .
1 100     .
end
format %tdMonth_dd,__CCYY date

[Sarah Edgington]

Try this:

bysort idn (day) : replace date=date[_n-1]+1 if _n>1

[Nick Cox]

Sarah Edgington gives excellent advice. Note that this is also covered in an FAQ https://www.stata.com/support/faqs/d...issing-values/