Generate variable with foreach loop with x-1 condition

[Anne Todd]

Hi all, using the data below, I am trying to figure out how to write a foreach loop that does what I've done in clunky fashion here.

Basically, I want to create a variable that captures whether a student was tested before a given age. But I also want to only keep students in the "0" group if they are never tested, or if they are not tested until they're 19. So the 0 condition is actually the same on all of these variables--the part I can't figure out is how to best tell Stata I want testedbefore_x to = 1 if testedx-1_w1 == 1, or testedx-2_w1 == 1, and so on down to 10. If anyone has any ideas I'd be very appreciative!

gen testedbefore_15 = .
replace testedbefore_15 = 0 if test == 0 | (inrange(age_firsttest, 19, 25)) 
replace testedbefore_15 = 1 if inlist(1, tested10_w1, tested11_w1, tested12_w1, tested13_w1, tested14_w1)

gen testedbefore_16 = .
replace testedbefore_16 = 0 if test == 0 | (inrange(age_firsttest, 19, 25)) 
replace testedbefore_16 = 1 if inlist(1, tested10_w1, tested11_w1, tested12_w1, tested13_w1, tested14_w1, tested15_w1)

gen testedbefore_17 = .
replace testedbefore_17 = 0 if test == 0 | (inrange(age_firsttest, 19, 25)) 
replace testedbefore_17 = 1 if inlist(1, tested10_w1, tested11_w1, tested12_w1, tested13_w1, tested14_w1, tested15_w1, tested16_w1)

gen testedbefore_18 = .
replace testedbefore_18 = 0 if test == 0 | (inrange(age_firsttest, 19, 25)) 
replace testedbefore_18 = 1 if inlist(1, tested10_w1, tested11_w1, tested12_w1, tested13_w1, tested14_w1, tested15_w1, tested16_w1, tested17_w1)

* Example generated by -dataex-. For more info, type help dataex
clear
input byte(tested10_w1 tested11_w1 tested12_w1 tested13_w1 tested14_w1 tested15_w1 tested16_w1 tested17_w1 tested18_w1 age_firsttest test) float(testedbefore_15 testedbefore_16 testedbefore_17 testedbefore_18)
0 0 0 0 0 0 1 0 0 16 1 . . 1 1
0 0 0 0 0 1 0 0 0 15 1 . 1 1 1
0 0 0 0 0 0 0 0 0 21 1 0 0 0 0
0 0 0 0 0 0 0 0 0 23 1 0 0 0 0
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 1 1 1 0 15 1 . 1 1 1
0 0 0 0 0 0 0 0 1 18 1 . . . .
0 0 0 0 0 0 0 0 0 22 1 0 0 0 0
0 0 0 1 0 0 0 0 1 13 1 1 1 1 1
0 0 1 0 0 0 0 0 0 12 1 1 1 1 1
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 17 1 . . . 1
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 17 1 . . . 1
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 1 0 0 1 0 0 0 0 11 1 1 1 1 1
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 18 1 . . . .
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 10 1 1 1 1 1
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 18 1 . . . .
0 0 0 0 0 0 0 1 0 17 1 . . . 1
0 0 0 0 0 0 0 1 0 17 1 . . . 1
0 0 0 0 0 0 1 1 0 16 1 . . 1 1
0 0 0 0 0 0 1 1 0 16 1 . . 1 1
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 20 1 0 0 0 0
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 18 1 . . . .
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
0 0 0 0 0 0 0 0 0  0 0 0 0 0 0
end

[Clyde Schechter]

Like most things in Stata, what is lengthy, repetitious, and circuitous with data in wide layout becomes simple and transparent if you -reshape- to long layout.

* Example generated by -dataex-. For more info, type help dataex
clear
input byte(tested10_w1 tested11_w1 tested12_w1 tested13_w1 tested14_w1 tested15_w1 tested16_w1 tested17_w1 tested18_w1 test)
0 0 0 0 0 0 1 0 0 1
0 0 0 0 0 1 0 0 0 1
0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 1 1 1 0 1
0 0 0 0 0 0 0 0 1 1
0 0 0 0 0 0 0 0 0 1
0 0 0 1 0 0 0 0 1 1
0 0 1 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 1 0 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 1 0 0 1 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 1
0 0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 1
0 0 0 0 0 0 0 1 0 1
0 0 0 0 0 0 0 1 0 1
0 0 0 0 0 0 1 1 0 1
0 0 0 0 0 0 1 1 0 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 1 1
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
end

gen `c(obs_t)' obs_no = _n
reshape long tested@_w1, i(obs_no) j(age)

by obs_no (age), sort: egen age_first_test = min(cond(tested_w1, age, .))
forvalues a = 15/18 {
    gen tested_before_`a' = age_first_test < `a'
}

I don't know what you will be doing next with this data. Because so few things in Stata work well in wide layout, most likely you are best off leaving the data long, as they are after this code. But if you know for a fact that your next steps will involve things that work better with wide data, you can just -reshape wide- at the end to get back to the original organization of the data.

[Anne Todd]

This is very clever--thank you Clyde.