seq | R Documentation |
Generate regular sequences. 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(...) ## Default S3 method: 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)
... |
arguments passed to or from methods. |
from, to |
the starting and (maximal) end values of the
sequence. Of length |
by |
number: increment of the sequence. |
length.out |
desired length of the sequence. A
non-negative number, which for |
along.with |
take the length from the length of this argument. |
Numerical inputs should all be finite (that is, not infinite,
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 seq_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.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.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
The methods seq.Date
and seq.POSIXt
.
:
,
rep
,
sequence
,
row
,
col
.
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)
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