st: Duplicate variable only if a previous variable has a certain value

[David de Jong <davidcdejong@gmail.com>]

Dear Statalist,

I'm trying to duplicate a set of variables (response times for a set
of trials) so that the original value is reproduced only if the trial
response was correct (which is indicated by an earlier set of
variables). If the trial response was incorrect the duplicated
variable should be missing.

Trials are numbered 21-164. Whether the trial was correct is stored in
variables correct21int-correct164int (0=correct, 1=incorrect, byte).
Response times are stored in variables rt21_w_sub400-rt164_w_sub400
(float).

So, for trial 21, I want to create a new variable called rt21corr that
is equal to rt21_w_sub400 if correct21int equals 0.

I've tried to do this with the following loop:

qui foreach v of var rt21_w_sub400-rt164_w_sub400 {
generate subinstr(`v',"_w_sub400","corr",1) = `v' if
subinstr(subinstr(`v',"_w_sub400","int",1),"rt","correct","1") == 0
}

In case -substr- wanted all of its constituent parts in quotes I tried this:

qui foreach v of var rt21_w_sub400-rt164_w_sub400 {
generate subinstr("`v'","_w_sub400","corr",1) = `v' if
subinstr("subinstr("`v'","_w_sub400","int",1)","rt","correct","1") ==
0
}

Both of these return the error message:
( invalid name

Can anyone help me figure out how to make this syntax work, or, if
there is a more elegant way to do what I hope to do.

Thanks a million,

David de Jong
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