Re: st: Date: Sat, 31 Mar 2007 12:56:37 +0200

[Phil Schumm <pschumm@uchicago.edu>]

On Mar 31, 2007, at 5:57 AM, Maarten Buis wrote:
> --- adiallo5@worldbank.org wrote:
> > My problem is that I need to return some colvector matrices in  
> > stata as variables to be used later. I don't know how to do that:
> >
> >         for (i=1; i<=cols(Z1); i++) {
> >            printf("i=%g\n",i)
> >            Z1i = Z1[1...,i]
> >            nomx = ("Z1i")
> >            stata("cap drop Z1i")
> > // I tried "cap drop Z1`i'", not working
> >            st_addvar("double",nomx)
> >            st_store(.,nomx,Z1i)
> >         }
> >
> > My matrice Z1 has 3 columns. I want to create Z11 Z12 Z13 as new  
> > variables in my datasets. But in Stata I only get Z1i as a variable.
> I am no mata expert, all I can tell you is what I found in the  
> helpfiles:
> I don't think it is necessary to loop here: -help mf_st_addvar-  
> tells me you can create multiple variables in one go and -help  
> mf_st_store- tells me you can store a matrix.

Maarten is of course correct here.  For example, suppose your matrix  
Z1 is numeric and has the same number of rows as your dataset in  
memory, and that you have no variables named Z11,...,Z1n.  In that  
case, all you need is the following:


    newvars = st_addvar("float", "Z1":+strofreal((1..cols(Z1))))
    st_store(.,newvars,Z1)


where you can replace the "float" in the call to -st_addvar()- with  
"double", if necessary.  If you cannot depend on your dataset having  
the same number of observations as Z1 has rows, then you could use  
something like


    if (st_nobs()<rows(Z1)) stata(sprintf("set obs %f",rows(Z1)))
    newvars = st_addvar("float", "Z1":+strofreal((1..cols(Z1))))
    st_store((1::rows(Z1)),newvars,Z1)


instead.  Production code would, of course, need to handle the  
possibility that the vars Z1,...,Zn already exist, and, in fact, in  
many cases you would want to be using temporary variables instead.


-- Phil

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