If loop in Mata

[Jay Rege]

Hey I want to write a Mata function with an if condition
function sum {
sum(x)
if sum(x) == 0 {
sum(y)

is that possible?

[Joseph Coveney]

Yes. It's possible. Here's one possibility.

.ÿversionÿ14.1

.ÿ
.ÿclearÿ*

.ÿsetÿmoreÿoff

.ÿ
.ÿlocalÿlinesizeÿ`c(linesize)'

.ÿsetÿlinesizeÿ78

.ÿ
.ÿmata:
-------------------------------------------------ÿmataÿ(typeÿendÿtoÿexit)ÿ----
:ÿmataÿsetÿmatastrictÿon

:ÿ
:ÿrealÿscalarÿfunctionÿsumif(realÿvectorÿX,ÿrealÿvectorÿY)ÿ{
>ÿÿÿÿÿÿÿÿÿrealÿscalarÿresult
>ÿÿÿÿÿÿÿÿÿresultÿ=ÿsum(X)
>ÿÿÿÿÿÿÿÿÿifÿ(resultÿ==ÿ0)ÿreturn(sum(Y))
>ÿÿÿÿÿÿÿÿÿelseÿreturn(result)
>ÿ}

:ÿ
:ÿXÿ=ÿ(1,ÿ2,ÿ3)

:ÿYÿ=ÿ(4,ÿ5,ÿ6)

:ÿsumif(X,ÿY)
ÿÿ6

:ÿ
:ÿXÿ=ÿ(0,ÿ0,ÿ0)

:ÿsumif(X,ÿY)
ÿÿ15

:ÿ
:ÿend
------------------------------------------------------------------------------

.ÿ
.ÿsetÿlinesizeÿ`linesize'

.ÿ
.ÿexit

endÿofÿdo-file


.

[Nick Cox]

It's not clear to me that you need a function for this. Consider

. mata
------------------------------------------------- mata (type end to exit) -
: x = (0,0,0)

: y = (1,2,3)

: result = sum(x) == 0 ? sum(y) : sum(x)

: result
  6

If you are determined to have a function, it can written just about as concisely:

 real myresult (real vector X, real vector Y) { 
     return(sum(X) == 0? sum(Y) : sum (X)) 
} 

myresult(x, y) 
  6

[Jay Rege]

Thanks! solved the problem!