How to loop over string content of a variable name?

[Maud Racapé]

Hi statalisters,

I created a loop to convert all the variables of my dataset containing binary text values such as No/Yes into numeric variables with 0/1 and No/Yes labels. This is an example because I think the content of the variable is not important here.

I named the numeric counterpart just adding _bis to the original variable name.

Now, I would like to delete the original variables if their numeric counterpart (variable_bis) exists.

Here's what I tried:

gen A=""
gen B=.
gen C=""
gen D=""
gen E=.
gen F="" ** this one contains text different from No/Yes so not converted in the loop
gen A_bis=.
gen C_bis=.
gen D_bis=.
 
foreach var of varlist  A-F {
drop `var' if `var'=="`var'"_bis
}

The code returns an "invalid synthax".

I tried a bunch of things including adding double quotes around the first `var' after if, single quotes around "`var'"_bis or trying to create a local macro with variable names but I was not able to solve the problem.
I guess this is a matter of properly calling the variable name and not its content but I can't figure out the place of the single or double quotes.

Can somebody help please?

Best,
Maud

[Roman Mostazir]

-drop if- works on observations not on variables. Use -drop `var'_bis - .Also you don't have B_bis variable, so loop might return error. Use 'capture' before drop:

foreach var of varlist  A-F {
capture drop `var'_bis
}

[Nick Cox]

#2 is closer in syntax to what you want, but if I understand correctly has the variable sets the wrong way round,

But to expand on Roman Mostazir 's point there is a big difference between the if command and the if qualifier.

Alternatively, you could turn this around.

foreach v of var *_bis {  

     local V = subinstr("`v'",  "_bis", "", .)
     capture drop `V'

}

[Roman Mostazir]

Apologies, I misread. Nick Cox is correct#3. You want to keep the original if "*_bis" exists and Nick has provided the solution for that.

[Maud Racapé]

Great thank you both!