Identify observations appeared in the previous year

[River Huang]

Dear All, I find this question here. The data set is

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte stkcd str5 year str8 BusinessInstitutionID byte want
4 "2011"  "10515981" .
4 "2012 " "10515981" 1
4 "2013 " "10515981" 1
4 "2013 " "10513314" .
4 "2014 " "10402864" .
4 "2014"  "10515981" .
4 "2014 " "10513314" 1
4 "2015 " "10516931" .
4 "2015"  "10514921" .
4 "2015"  "10515981" 1
4 "2015"  "10513314" 1
4 "2016"  "10516535" .
4 "2016"  "10519103" .
4 "2016"  "10516931" 1
4 "2016"  "10402864" .
4 "2016"  "10515981" 1
4 "2017 " "10520158" .
4 "2017"  "10519103" 1
4 "2017"  "10402864" 1
4 "2017"  "10513235" .
4 "2017 " "10520422" .
end

For each stkcd and each year, I'd like to identify whether `BusinessInstitutionID' has appeared in the previous year. If yes, return 1, otherwise missing data (zero is also fine). The variable `want' is the desired outcome. Thanks.

[Maarten Buis]

destring year, replace
bys stkcd BusinessInstitutionID (year): gen wanted = (year[_n-1] == (year - 1))
list , sepby(BusinessInstitutionID)

[River Huang]

Dear Maarten, Thanks a lot for this helpful suggestion.

[Nick Cox]

An important detail is implicit here. Maarten Buis created the indicator as 1 if true and 0 if false. That's much more useful than a variable that is 1 if true and missing if false.

[River Huang]

Dear Nick, I agree with your point.