A.4 기정의 상수 (Predefined Constant)
R에는 다음과 같은 상수들(contants)이 있다.
TRUE # true, 1 as.numeric
FALSE # false, 0 as.numeric
NULL # no element
Inf # +Infinity
-Inf # -Infinity
NaN # Not a Number
NA # Not Available
NA_integer_ # integer type NA
NA_real_ # real type NA
NA_complex_ # complex type NA
NA_character_ # character type NA
LETTERS # A to Z
letters # a to z
month.abb # Jan to Dec
month.name # January to December
pi # 3.14159...