| NumericConstants {base} | R Documentation |
How R parses numeric constants.
R parses numeric constants in its input in a very similar way to C99 floating-point constants.
Inf and NaN are numeric constants (with
typeof(.) "double"). In text input (e.g. in
scan and as.double), these are recognized
ignoring case as is infinity as an alternative to Inf.
NA_real_ and NA_integer_ are constants of
types "double" and "integer" representing missing
values. All other numeric constants start with a digit or period and
are either a decimal or hexadecimal constant optionally followed by
L.
Hexadecimal constants start with 0x or 0X followed by
a nonempty sequence from 0-9 a-f A-F . which is interpreted as a
hexadecimal number, optionally followed by a binary exponent. A binary
exponent consists of a P or p followed by an optional
plus or minus sign followed by a non-empty sequence of (decimal)
digits, and indicates multiplication by a power of two. Thus
0x123p456 is 291 * 2^456.
Decimal constants consist of a nonempty sequence of digits possibly
containing a period (the decimal point), optionally followed by a
decimal exponent. A decimal exponent consists of an E or
e followed by an optional plus or minus sign followed by a
non-empty sequence of digits, and indicates multiplication by a power
of ten.
Values which are too large or too small to be representable will
overflow to Inf or underflow to 0.0.
A numeric constant immediately followed by i is regarded as an
imaginary complex number.
An numeric constant immediately followed by L is regarded as an
integer number when possible (and with a warning if it
contains a ".").
Only the ASCII digits 0–9 are recognized as digits, even in languages which have other representations of digits. The ‘decimal separator’ is always a period and never a comma.
Note that a leading plus or minus is not regarded by the parser as part of a numeric constant but as a unary operator applied to the constant.
When a string is parsed to input a numeric constant, the number may or may not be representable exactly in the C double type used. If not one of the nearest representable numbers will be returned.
R's own C code is used to convert constants to binary numbers, so the
effect can be expected to be the same on all platforms implementing
full IEC 600559 arithmetic (the most likely area of difference being
the handling of numbers less than .Machine$double.xmin).
The same code is used by scan.
Quotes for the parsing of character constants,
2.1 typeof(2) sqrt(1i) # remember elementary math? utils::str(0xA0) identical(1L, as.integer(1)) ## You can combine the "0x" prefix with the "L" suffix : identical(0xFL, as.integer(15))