Panel Data Cleaning Question: Replacing Variable(s) Based on a Previous Observation

[Jason Yang]

Hello (and thank you in advance for any help),

I have a panel dataset (with variable id as the cross-section and time as the time dimension). I have attached example data to this post. The variable Mark currently indicates the first time the id gets a treatment. However, I want to replace "Mark" such that all times after the first treatment (for each id) also receive a "1" and that all values prior to the first treatment get a "0". For example, for id 1 and time 4, there should be a "1" in Mark. For id 2, there should be a "1" in Mark for times 3 and 4 also.

Can anyone help with generating a code that will solve this problem (as I will apply it to a larger dataset)? Thank you for any help you can provide!

* Example generated by -dataex-. For more info, type help dataex
clear
input byte(id time Mark)
1 1 .
1 2 .
1 3 1
1 4 .
2 1 .
2 2 1
2 3 .
2 4 .
end

[Andrew Musau]

bys id (time): replace Mark= Mark[_n-1] if missing(Mark) & !missing(Mark[_n-1])
replace Mark= !Mark if missing(Mark)

[Jason Yang]

This was exactly what I was looking for, thank you so much!

[Andrew Musau]

Also note that

bys id (time): replace Mark=sum(Mark)

will do it as missing values will be summed as zeros.

[Jason Yang]

That's a great alternative way. Thank you again!