RE: st: RE: scalar do not allow -if-

[Nick Cox <n.j.cox@durham.ac.uk>]

Yes and no; the code is good, but the commentary could be misleading. 

You can certainly use -cond()- to define these scalars, as others have already pointed out in this thread. 

But its role is not analogous to that of the -if- qualifier. -if- qualifiers apply conditionally to a subset of observations (which may be empty or the whole set), but no such notion applies to scalars. 

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

Sergiy Radyakin

the scalar version of -if- is cond():
scalar hig = cond(w2>w1,cond(w3>w2,3,2),cond(w3>w1,3,1))
although if in your example you had w1,w2,...w100, you wouldn't want
to write anything like the above.
you would then program one -forvalues- loop and one -if- branch that
updates the index of the max element.

On Wed, Nov 17, 2010 at 11:11 AM, Nick Cox <n.j.cox@durham.ac.uk> wrote:
> A command
>
> ... if <condition>
>
> applies observation by observation and can not be what you want.
>
> I guess that you want
>
> if (w1 > w2) & (w1 > w3) {
>        scalar hig = 1
> }
> else if (w2 > w1) & (w2 > w3) {
>        scalar hig = 2
> }
> else if (w3 > w1) & (w3 > w2) {
>        scalar hig = 3
> }
>
> These sound like "w1 biggest", "w2 biggest", "w3 biggest". If there are any ties w1 == w2 | w2 == w3 your scalar will be undefined. (I've corrected what looks like a typo in your code, but not this problem with ties, which is perhaps unlikely.)

Tomas Lind

> In a small simulation I generate data and analyze them with 3 regression methods. In the bottom of the loop I save (among other things)
>
> scalar b2   = exp(_b[x])        // beta
>
> and then put the -scalar- values into a variable in a dataset where I collect the results from the 1000 simulated datasets. For example
>
> quietly replace b2=scalar(b1) in `i'
>
>
> That works fine. Now I want to calculate "hig" (in the bottom of the loop) and save it in the dataset with aggregated data (where w1, w2, w3 are -scalars-).
>
> scalar hig = 1  if (w1 > w2) & (w1 > w3)
> scalar hig = 2  if (w2 > w1) & (w2 > w3)
> scalar hig = 3  if (w3 > w1) & (w3 > w1)
>
> However, -if- is not allowed in combination with  -scalar-.



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