If condition with value labels

[Mahdi Jafari]

Is it possible to impose if condition with value labels ?
for example :

lab define gender 1 "Male" 2 "Female"
lab values sex gender
drop if sex == "Male"   // or drop if sex==Male

[Joseph Coveney]

drop if sex == "Male":gender

[Mahdi Jafari]

drop if sex == "Male":gender

Thanks.

[Daniel Schaefer]

Why does the colon notation at the end work? Is this syntax unique to labels, or are we leveraging a more general feature of the language? It almost looks like the colon here is dereferencing a value on the gender object using "Male" as a key, but if so this feels idiosyncratic to the way the rest of the language works.

[daniel klein]

Why does the colon notation at the end work? Is this syntax unique to labels [...]?

The syntax is unique to value labels used in expressions. This feature is demonstrated in Higbee (2004).

I cannot speak to the underlying mechanics but if it is something like a lookup, it does not handle collisions well; only the first matching value is returned:

. label define foolbl 42 "foo" 73 "foo"

. local not_73 = "foo":foolbl

. display `not_73'
42

For similar functionality (and same behavior for duplicate labels) in Mata, see st_vlsearch().


Higbee, K. 2004. Stata tip 14: Using value labels in expressions. The Stata Journal, 4(4), pp. 486--487.