codebook is a great command in Stata. It describes data contents but also simply identifies unique values
sysuse auto, clear
codebook mpg, compact
Number of unique values of mpg is 21. Looking at the help of the command, it does not seem possible to store this value. Am I wrong?
I am aware of other ways to compute the number of unique values in Stata, but it would be so convenient to add this feature to the codebook command.
You can easily write a wrapper for codebook that uses Nick's distinct command from SSC to store the info you want as scalar(s).
In my experience, this wrapper approach has proven to be much more effective than asking the nice folks at StataCorp to change their command on an internet forum that they do not participate in.
Here's an example:
* (1) You can stick this into a file called mycodebook.ado in
* /ado/personal (use adopath to see exact location)
capture program drop mycodebook
program mycodebook, rclass
syntax [varlist] [if] [in][, *]
codebook `varlist' `if' `in', `options'
capture ssc install distinct
foreach var of varlist `varlist' {
qui distinct `var' `if' `in'
return scalar nv_`var' = r(ndistinct)
}
end
* (2) example with mycodebook
sysuse auto, clear
mycodebook price mpg rep78 if foreign==0, compact
return list
This last part will give you:
. mycodebook price mpg rep78 if foreign==0, compact
Variable Obs Unique Mean Min Max Label
----------------------------------------------------------------------------------
price 52 52 6072.423 3291 15906 Price
mpg 52 17 19.82692 12 34 Mileage (mpg)
rep78 48 5 3.020833 1 5 Repair Record 1978
----------------------------------------------------------------------------------
. return list
scalars:
r(nv_rep78) = 5
r(nv_mpg) = 17
r(nv_price) = 52
You can then do things like (or whatever it is you want to do with these):
gen x=r(nv_rep78)