Generate variable with the name of another variable

[Esteban Jara]

Hello. In a dataset like this:

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(x1 x2 z)
10 20 20
34 14 34
end

I need to create a variable this_is that indicates which variable, x1 or x2, matches in value with z

In this case, the result should be:

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(x1 x2 z) str2 this_is
10 20 20 "x2"
34 14 34 "x1"
end

How can I do it? Thanks

[Rich Goldstein]

what do you want the new variable to be is x1=z AND x2=z?

[Esteban Jara]

Sorry if I didn't make myself understood. In this example, in the first row since z = x2 then the result of this_is is "x2"; in the second row, since z = x1 then the result of this_is is "x1".

[Rich Goldstein]

I do understand that but apparently you did not understand what I meant: what if x1=10 and x2=10 and z=10 - then what should your new variable be?

[Esteban Jara]

Oh, I understand. For what I need, either of the two results works: x1 or x2. If you could include the instruction that the result be the first variable (from left to right), in this case x1, that would be great. Thanks a lot

[Rich Goldstein]

try the following (this could be compressed to one line using the cond() function):

gen str this_is=""
replace this_is="x2" if x2==z
replace this_is="x1" if x1==z

[Nick Cox]

gen this_is = cond(z == x1, "x1", "x2")

or paranoid code

gen this_is = cond(z == x1, "x1", cond(z == x2, "x2", "???????"))

[Esteban Jara]

Well, I was wrong in assuming that it would be understood that what I need is for general cases, not for specifically these two variables x1 and x2. Basically I would like to know if there is a command, or a more general trick, that generates values based on the names of other variables. And now, yes, I apologize for not making myself understood correctly.

[Nick Cox]

A more abstract formulation is this:

initialise a string variable with empty

loop over some other variables:

replace string variable with variable name if some condition is true

As Rich Goldstein flagged, a key detail is what we want to happen if there are multiple finds, e.g. to record first or last instance found or all instances found.

A recent paper in the Stata Journal discusses row-wise examples.

[Esteban Jara]

Thanks to both