A loop problem

[Xinkai Mao]

Dear all:

I have a problem when dealing with my data, for one variable. There is only "1","2", and "0", I want to find the first "1", and then find the next "2", then find the next "1",and so on like the following example:
from the right to the left
0 0
0 0
1 1
1 0
1 0
1 0
0 0
1 0
2 2
2 0
1 1
1 0

Thank you!
Best wishes

[Clyde Schechter]

* Example generated by -dataex-. For more info, type help dataex
clear
input byte v1
0
0
1
1
1
1
0
1
2
2
1
1
end

gen wanted = v1 in 1
forvalues i = 2/`=_N' {
    replace wanted = 1 if inlist(wanted[_n-1], 0, 2) & v1 == 1 in `i'
    replace wanted = 2 if wanted[_n-1] == 1 & v1 == 2 in `i'
    replace wanted = wanted[_n-1] if missing(wanted) in `i'
}

gen run = sum(wanted != wanted[_n-1])
sort run, stable
by run: replace wanted = 0 if _n > 1

In the future, when showing data examples, please use the -dataex- command to do so, as I have here. If you are running version 17, 16 or a fully updated version 15.1 or 14.2, -dataex- is already part of your official Stata installation. If not, run -ssc install dataex- to get it. Either way, run -help dataex- to read the simple instructions for using it. -dataex- will save you time; it is easier and quicker than typing out tables. It includes complete information about aspects of the data that are often critical to answering your question but cannot be seen from tabular displays or screenshots. It also makes it possible for those who want to help you to create a faithful representation of your example to try out their code, which in turn makes it more likely that their answer will actually work in your data.

[Xinkai Mao]

* Example generated by -dataex-. For more info, type help dataex
clear
input byte v1
0
0
1
1
1
1
0
1
2
2
1
1
end

gen wanted = v1 in 1
forvalues i = 2/`=_N' {
replace wanted = 1 if inlist(wanted[_n-1], 0, 2) & v1 == 1 in `i'
replace wanted = 2 if wanted[_n-1] == 1 & v1 == 2 in `i'
replace wanted = wanted[_n-1] if missing(wanted) in `i'
}

gen run = sum(wanted != wanted[_n-1])
sort run, stable
by run: replace wanted = 0 if _n > 1

In the future, when showing data examples, please use the -dataex- command to do so, as I have here. If you are running version 17, 16 or a fully updated version 15.1 or 14.2, -dataex- is already part of your official Stata installation. If not, run -ssc install dataex- to get it. Either way, run -help dataex- to read the simple instructions for using it. -dataex- will save you time; it is easier and quicker than typing out tables. It includes complete information about aspects of the data that are often critical to answering your question but cannot be seen from tabular displays or screenshots. It also makes it possible for those who want to help you to create a faithful representation of your example to try out their code, which in turn makes it more likely that their answer will actually work in your data.

Thank you for your help! Clyde. I will use the -dataex- in the future. I really appreciate it.