seq is a standard generic with a
default method. seq.int is a primitive which can be
much faster but has a few restrictions. seq_along and
seq_len are very fast primitives for two common cases.
seq(...)
"seq"(from = 1, to = 1, by = ((to - from)/(length.out - 1)), length.out = NULL, along.with = NULL, ...)
seq.int(from, to, by, length.out, along.with, ...)
seq_along(along.with)
seq_len(length.out)1 unless just from is supplied as
an unnamed argument.seq and seq.int will be
rounded up if fractional.seq.int and the default method of seq for numeric
arguments return a vector of type "integer" or "double":
programmers should not rely on which.seq_along and seq_len return an integer vector, unless
it is a long vector when it will be double.
NaN or NA). The interpretation of the unnamed arguments of seq and
seq.int is not standard, and it is recommended always to
name the arguments when programming.
seq is generic, and only the default method is described here.
Note that it dispatches on the class of the first argument
irrespective of argument names. This can have unintended consequences
if it is called with just one argument intending this to be taken as
along.with: it is much better to use seg_along in that
case.
seq.int is an internal generic which dispatches on
methods for "seq" based on the class of the first supplied
argument (before argument matching).
Typical usages are
seq(from, to) seq(from, to, by= ) seq(from, to, length.out= ) seq(along.with= ) seq(from) seq(length.out= )The first form generates the sequence
from, from+/-1, ..., to
(identical to from:to). The second form generates from, from+by, ..., up to the
sequence value less than or equal to to. Specifying to -
from and by of opposite signs is an error. Note that the
computed final value can go just beyond to to allow for
rounding error, but is truncated to to. (‘Just beyond’
is by up to $1e-10$ times abs(from - to).)
The third generates a sequence of length.out equally spaced
values from from to to. (length.out is usually
abbreviated to length or len, and seq_len is much
faster.)
The fourth form generates the integer sequence 1, 2, ...,
length(along.with). (along.with is usually abbreviated to
along, and seq_along is much faster.)
The fifth form generates the sequence 1, 2, ..., length(from)
(as if argument along.with had been specified), unless
the argument is numeric of length 1 when it is interpreted as
1:from (even for seq(0) for compatibility with S).
Using either seq_along or seq_len is much preferred
(unless strict S compatibility is essential).
The final form generates the integer sequence 1, 2, ...,
length.out unless length.out = 0, when it generates
integer(0).
Very small sequences (with from - to of the order of $10^{-14}$
times the larger of the ends) will return from.
For seq (only), up to two of from, to and
by can be supplied as complex values provided length.out
or along.with is specified. More generally, the default method
of seq will handle classed objects with methods for
the Math, Ops and Summary group generics.
seq.int, seq_along and seq_len are
primitive.
seq.Date and seq.POSIXt.seq(0, 1, length.out = 11)
seq(stats::rnorm(20)) # effectively 'along'
seq(1, 9, by = 2) # matches 'end'
seq(1, 9, by = pi) # stays below 'end'
seq(1, 6, by = 3)
seq(1.575, 5.125, by = 0.05)
seq(17) # same as 1:17, or even better seq_len(17)
Run the code above in your browser using DataLab