seq {base}

Sequence Generation

Description

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.

Usage

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

...

arguments passed to or from methods.

from, to

the starting and (maximal) end values of the sequence. Of length 1 unless just from is supplied as an unnamed argument.

by

number: increment of the sequence.

length.out

desired length of the sequence. A non-negative number, which for seq and seq.int will be rounded up if fractional.

along.with

take the length from the length of this argument.

Details

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 10^{-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.

Value

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.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

The methods seq.Date and seq.POSIXt.

:, rep, sequence, row, col.

Examples

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)