number of variables in varlist with -describe-

[Dirk Enzmann]

The help of -describe- states that the number of variables in varlist will be stored in r(k). However, when I try

sysuse auto, clear
qui d
di `r(k)'      // r(k)=12 -- OK
foreach v of varlist _all {
   clonevar clone_`v' = `v'
}
qui d
di `r(k)'      // r(k)=24 -- OK
qui d clone_*
di `r(k)'      // r(k)=24 -- but should be 12

the last display command should show 12 (as I would expect from the help of -describe-) -- not 24. Previously (as of 2011) the -describe- command still seemed to work as I would expect, see Nick's answer in the old Statalist: https://www.stata.com/statalist/arch.../msg00744.html .

What am I doing wrong or what has changed, since?

[Mike Lacy]

Thanks for bringing this up. I noticed this fact a few years ago but had forgotten: The display from -describe- conforms to the varlist specfied, but r(k) reflects the entire data set, e.g., try -describe weight- and one gets r(k) = 12. The help description is perhaps ambiguous about the intended behavior as regards r():

describe stores the following in r():

Scalars
r(N) number of observations
r(k) number of variables
r(width) width of dataset
r(changed) flag indicating data have changed since last save

[Dirk Enzmann]

Thanks for granting that my interpretation of the help of -describe- is at least understandable (I am in good company if Nick stumbled about his, as well).

Thus, -describe- can't be used directly to count the number of variables in a var*-list. One solution would be

qui ds clone*
di `: word count `r(varlist)''

In my example above this would result in the expected number of 12.

[Mike Lacy]

I didn't have to grant anything <grin>. I take your side and I think the documentation is not good here.