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# RE: st: mata for-if-else

 From "Nick Cox" To Subject RE: st: mata for-if-else Date Wed, 14 Apr 2010 11:44:58 +0100

```There are several mistakes here.
The syntax of -for- requires semi-colons.
Testing for equality requires == not =.
Mata has no equivalent of Stata's -if- qualifier.

Positively, this codes more congenially using ?:

Try

for(i=1; i<1001; i++) {
a[i]  = b[i] == 1 ? 2 : 3
}

Nick
n.j.cox@durham.ac.uk

Abhimanyu Arora

Thanks Sabrina, but unfortunately the problem persists.

If I understood correctly what you meant, I used the following:

mata

a=J(1000,1,1)

for(i=1,i<1001,i++) {
a[i]=2 if b[i]==1
a[i]=3 if b[i]!=1

}

a
end

Sabrina Carrossa

I am not sure, but I guess you'd better use the "if qualifier" instead
of the "if-else" command.

On 14 April 2010 10:54, Abhimanyu Arora

> I have simplified my problem to a large extent, but essentially has to
do
> with using for-if-else commands in mata. I would like to create a
matrix
'a'
> whose values depend on an existing matrix 'b' (both are 1000X1 vectors
to
be
> precise). I need to tell mata the dimension of a first. But all I get
after
> executing the commands below is the original vector 'a'. What could be
the
> possible error? I have tried adding and removing braces but it is not
> working...
>
>
>
>
> a=J(1000,1,.)
> for(i=1,i<1001,i++) {
> if (b[i]==1){
> a[i]=2
> }
> else {a[i]=3
> }
> }
> a
> end
>

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