How to transform a bilateral variable into a unilateral variable

[marie nour]

Dear Stata users,

I am trying to figure out how to solve the following problem:
I have bilateral variables (called agreement_1, agreement_2, etc.) that equals 1 when two countries belong to the same agreement. However, I would like to have a dummy variable that indicates whether the second country belongs to a specific agreement no matter if its partner country (country 1) belongs to the agreement or not.
Here is an example:

 input str3 country1 str3 country2 agreement_1 agreement_2
"BDI" "RWA" 1 0
"BDI" "ZAF" 0 1
"FRA" "RWA" 0 0
"RWA" "BDI" 1 0
end

So I want to have a unilateral variable (called agreement_1_country2) which will equal 1 for the first, third and fourth line, meaning whenever the country2 is RWA or BDI since we know that these countries belong to the agreement_1.
I was thinking of using the command tab to obtain all the distinct values for country2:

 tab country2 if agreement_1 == 1

but then I don't know what to eventually create the new variable agreement_1_country2.

One thing I want to add, is that I don't necessarily need to generate the unilateral variable in my database, I just need it in memory to create additional variables later in my code using this unilateral variable as a condition.

Thank you in advance.
Marie

[Andrew Musau]

Several ways to do this, here is one.

levelsof country1, local(X) separate(|) clean
gen wanted= regexm(country2 , "(`X')")

Res.:

. l

     +----------------------------------------------------+
     | country1   country2   agreem~1   agreem~2   wanted |
     |----------------------------------------------------|
  1. |      BDI        RWA          1          0        1 |
  2. |      BDI        ZAF          0          1        0 |
  3. |      FRA        RWA          0          0        1 |
  4. |      RWA        BDI          1          0        1 |
     +----------------------------------------------------+

[Andrew Musau]

It appears that I missed this

However, I would like to have a dummy variable that indicates whether the second country belongs to a specific agreement no matter if its partner country (country 1) belongs to the agreement or not.

You want first

levelsof country1 if agreement_1, local(X) separate(|) clean

[marie nour]

Dear Andrew,

Thank you, it works. There was just a small mistake in the code, instead of country1, I used country2:

levelsof country2 if agreement_1, local(X) separate(|) clean

.

Best