R: Sequence Generation

seq {base} | R Documentation

## 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 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.

### 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)

[Package base version 4.0.5 Index]