Mata Program which either works for a Mata matrix or for a Stata variable

[Anika Bittner]

Dear Statalists,

For an assignment I need to write a Mata program that recognises the kind of input and either runs the function for a Mata matrix or for the Stata variable that is specified in the function.

Here you see the (simplified) program, that only works for Mata matrix:

clear mata
mata  
real matrix function posmean (real vector x) {    
        real vector A, B
        
        A = select(x, x[1,.]:>0)
        B = mean(A')                            
        return(B)
    }
    
x1 = (1, 2, -3, 4, 5, -6)
x2 = (1 \ 2 \ 3 \ -4 \ 4)
posmean(x1)
posmean(x2)
}
end

Here you see the (simplified) program, that only works for Stata variable:

sysuse auto, clear
clear mata
mata:
real matrix function posmean(transmorphic vector x) {
        real vector C, D
        
        st_view(L=.,.,x)
        C = select(L,L[.,.]:>0)
        D = mean(C)    
        return(D)
}
posmean("price")
end

Now I need one Mata program that either works for a Mata matrix or for a Stata variable. I tried several things but nothing worked. Therefore, I need your help!

Thank you very much in advance!

Best wishes
Anika

[Nick Cox]

As this is an assignment, I hint only at passing the function a name and then testing inside the function what exists. You don't say what should happen if both the variable and the matrix already exist.

[Anika Bittner]

Dear Nick,

Thank you for your answer! I tested the function with 'if (eltype(x)=="string"') and it works.
Don't know if this is exactly what you meant but it serves its purpose.

I feel really blessed that you answered my question. You kind of a hero for Stata!

Best wishes
Anika