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=)
seq(along=)
seq(from)
```

### Arguments

 `from` starting value of sequence. `to` (maximal) end value of the sequence. `by` increment of the sequence. `length` desired length of the sequence. `along` 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`.

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

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

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

The result is of `mode` `"integer"` if `from` is (numerically equal to an) integer and `by` is not specified.

### References

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

The method `seq.POSIXt`.

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

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

### 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
```

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