seq {base} | R Documentation

## Sequence Generation

### Description

Generate regular sequences.

### Usage

    from:to
       a:b

    seq(from, to)
    seq(from, to, by= )
    seq(from, to, length.out= )
    seq(along.with= )
    seq(from)

### Arguments

`from` | starting value of sequence.
`to` | (maximal) end value of the sequence.
`by` | increment of the sequence.
`length.out` | desired length of the sequence.
`along.with` | take the length from the length of this argument.
`a,b` | `factor`s of same length.

### Details

The binary operator `:` has two meanings: for factors `a:b` is equivalent to `interaction(a, b)` (except for labelling by `la:lb` not `la.lb`). For numeric arguments `a:b` is equivalent to `seq(from=a, to=b)`.

The interpretation of the unnamed arguments of `seq` is not standard, and it is recommended always to name the arguments when programming.

Function `seq` is generic, and only the default method is described here.

The operator `:` and the `seq(from, to)` form generate the sequence `from, from+1, ..., 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.

The third generates a sequence of `length.out` equally spaced values from `from` to `to`.

The fourth form generates the sequence `1, 2, ..., length(along.with)`.

The last generates the sequence `1, 2, ..., length(from)` (as if argument `along` 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).

If `from` and `to` are factors of the same length, then `from : to` returns the “cross” of the two.

Very small sequences (with `from - to` of the order of 10^{-14} times the larger of the ends) will return `from`.

### Value

Currently, the default method returns a result of storage mode `"integer"` if `from` is (numerically equal to an) integer and, e.g., only `to` is specified, or also if only `length` or only `along.with` is specified. Note: this may change in the future and programmers should not rely on it.

### References

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

### See Also

The method `seq.POSIXt`.

`rep`, `sequence`, `row`, `col`.

As an alternative to using `:` for factors, `interaction`.

For `:` used in the formal representation of an interaction, see `formula`.

### Examples

    1:4
    pi:6 # float
    6:pi # integer

    seq(0,1, length=11)
    seq(rnorm(20))
    seq(1,9, by = 2) # match
    seq(1,9, by = pi)# stay below
    seq(1,6, by = 3)
    seq(1.575, 5.125, by=0.05)
    seq(17) # same as 1:17

    for (x in list(NULL, letters[1:6], list(1,pi)))
      cat("x=",deparse(x),";  seq(along = x):",seq(along = x),"\n")

    f1 <- gl(2,3); f1
    f2 <- gl(3,2); f2
    f1:f2 # a factor, the "cross"  f1 x f2

[Package base version 2.3.1 Index]