Only Keeping Children if Their Parents are in the Survey

[Cora Touchstone]

Hi All,

I am trying to make a child file where I only keep observations of those children who have parents in the survey. First, I will show how I made a "father file," which only keeps ID's which can be found in the "ID_F" column.

* Example generated by -dataex-. To install: ssc install dataex
clear
input str5(ID Income ID_F)
"A1" "10" "D4"
"B2" "11" "." 
"C3" "12" "A1"
"D4" "13" "B2"
"E5" "14" "A1"
end

To only keep IDs found in the ID_F column, I used the lines:

expand 2, gen(ex)
replace ID = ID_F if ex
bys ID (ex): keep if ex[_N]
drop if ex == 1
drop ex


But now I want to only keep IDs who have an input in "ID_F" or "ID_M" (not necessarily both) where the value for "ID_F" or "ID_M" is also in the ID column. Here is a data example:

* Example generated by -dataex-. To install: ssc install dataex
clear
input str5(ID Revenue ID_F ID_M)
"A1" "10" "Z4" "Z5"
"B2" "11" "."  "C3"
"C3" "12" "A1" "D4"
"D4" "13" "."  "M3"
"E5" "14" "A1" "C3"
end

In this case, I only want to keep observations B2, C3, and E5, since each have a father or mother that is also in the survey. Any guidance would be much appreciated.

Best,
Cora

[William Lisowski]

To the either set of code given in post #2 of your previous topic at

https://www.statalist.org/forums/for...running-slowly

add

keep if parents_present

[Romalpa Akzo]

Try below code. Please share out the observed speed when applying it to your actual data.

expand 2, gen(ex)

replace ID = ID_F if ex
bys ID (ex): gen match_F = ex[_N]

replace ID = ID_M if ex
bys ID (ex): gen match_M = ex[_N]

keep if (match_F | match_M) & !ex
drop ex