StackOverflow defines the following on-topics:
a specific programming problem, or
a software algorithm, or
software tools commonly used by programmers; and is
a practical, answerable problem that is unique to software development
SO does not define programming per se, so we'd have to go elsewhere. According to Wikipedia,
Computer programming (often ...
The issue of an R-specific SE now appears to be moot, as judging from the link the proposal has been closed with the message:
The R community embraced Stack Overflow as The place
for R support and went on to gain a strong following on our Cross
Validated site. – Robert Cartaino♦ 2 hours ago
(Robert Cartaino is "the Director of ...