Names of st_tempname() temporal variables

[Nicolas Suarez]

Hi everyone,

In Mata, I am trying to work with temporary variables, but I am having trouble accesing them from Stata. For instance, if I use st_tempname() to create one temporary variable, "temp_var", the code works in creating the temporary variable, but I can't access it from Stata as `temp_var', only with the temporary name of the first variable, __000000.

sysuse auto, clear
mata: st_addvar("double", temp_var=st_tempname())
mata: st_store(.,temp_var, rnormal(74,1,10,100))

summ __000000
summ `temp_var'

If I wanted to create even more temporary variables, st_tempname()'s documentation doesn't even mention how you can name them. For instance, here I create 11 temporary variables, and the only way to access them is with their names, __000000 to __00000A.

mata: idx=st_addvar("double", st_tempname(11))
mata: st_store(.,idx, rnormal(74,11,10,100))
summ __*

How can I call these variables from Stata? Calling them as __0000* is not ideal, since after 10 variables the naming pattern changes to letters (__00000A), and these names will change if there are other temporary variables already defined.

[Joseph Coveney]

In Mata, I am trying to work with temporary variables, but I am having trouble accesing them from Stata. . . .How can I call these variables from Stata?

You get their names via the st_varname() function.

Feed to that function the variable index vector that you get from st_addvar(), prepend any names that you want to them, and then send them to Stata in a local macro via the st_local() function.

Like the following (I've limited it to three temporary variables instead of eleven for brevity).

version 18

clear *

set seed 1617787289

quietly sysuse auto

mata {

    Idxs = st_addvar("double", st_tempname(3))
    st_store(., Idxs, rnormal(st_nobs(), cols(Idxs), 10, 100))

    for (i=1; i<=cols(Idxs); i++) {
        st_local("temp_var" + strofreal(i), st_varname(Idxs[i]))
    }
}

display in smcl as result "`temp_var1'", "`temp_var2'", "`temp_var3'"

forvalues i = 1/3 {
    summarize `temp_var`i''
}

exit

[Nicolas Suarez]

Thank you Joseph, this is a great solution to my problem!

Best,
Nicolas.

[Nicolas Suarez]

Hi everyone,

If anyone else comes across this question, I found an alternative solution, similar to what Joseph did here, if you don't need the individual names of these variables:

sysuse auto, clear
mata{
var_indexes=st_addvar("double", st_tempname(11))
st_store(.,var_indexes, rnormal(st_nobs(),11,10,100))
mata: st_local("varlist",invtokens(st_varname(var_indexes)))
}
describe `varlist'

The first line assign column indexes to these temporary variables, the second line put the values into Stata, and the third line gets the name with st_varname() as a string vector. Since we can't pass that to Stata as a local variable, invtokens() concatenates the elements of this vector, separated by spaces.