Equivalent function of R's "%in%" for Stata

Is there an equivalent function of "%in%" from R for Stata?

As already mentioned, it's hard to tell what you need from the question. inlist() might work, or it might not depending on the setting.

I find that Stata's macro lists functions are invaluable. Store your list in a macro (local or global) and then a suite of useful commands are available:

local list   a b c d d e 
local search c 
local search_in_list : list search in list
di    `search_in_list'

These can be calculated on the fly:

if `: list search in list' {
    actions if true
}

Stata does not offer the same flexible tool, but inlist will cover the basic operation that you might be looking for, as in count if inlist(country,"FR","US","DE").

working with lists proper is one way, you could also just treat the rhs like a string and treat the lhs as a regex, use regexm()