Finding out when same entity/unit changes codes across years

[Saul Gabriel]

Greetings Stata-user community,

I have a thorn-in-my-side with a variable (sysschoolid) that may and can change across time for the same entity (schools; school2 variable); see data example below.

The question I have is how to loop through the entire dataset to find out when the code changes for the same entity across time.
I am sure there is a rather simple line or group of lines that can help.

Thanks in advance,
Saul

* Example generated by -dataex-. For more info, type help dataex
clear
input str9 sysschoolid str40 school2 double year
"601:103"  "appling county high school" 2006
"601:103"  "appling county high school" 2007
"601:103"  "appling county high school" 2008
"601:103"  "appling county high school" 2009
"601:103"  "appling county high school" 2010
"601:103"  "appling county high school" 2011
"601:103"  "appling county high school" 2012
"601:103"  "appling county high school" 2013
"601:103"  "appling county high school" 2014
"601:103"  "appling county high school" 2015
"601:103"  "appling county high school" 2016
"601:103"  "appling county high school" 2017
"601:103"  "appling county high school" 2018
"601:103"  "appling county high school" 2019
"601:103"  "appling county high school" 2020
"601:2050" "appling county high school" 2004
"601:2050" "appling county high school" 2005
end

[Rich Goldstein]

If I understand you correctly, there is no need for a loop; try this:

bys school2 (year): gen change=sys!=sys[_n-1] & _n>1

[Saul Gabriel]

Rich Goldstein Thanks for this!! This is indeed what I need. I now need to add a qualifier so that schools that were not in existence (or for which no data were collected) are not coded as changed...