# Colon: Colon Operator

## Description

Generate regular sequences.

## Usage

 ```1 2``` ```from:to a:b ```

## Arguments

 `from` starting value of sequence. `to` (maximal) end value of the sequence. `a, b` `factor`s of the same length.

## Details

The binary operator `:` has two meanings: for factors `a:b` is equivalent to `interaction(a, b)` (but the levels are ordered and labelled differently).

For other arguments `from:to` is equivalent to `seq(from, to)`, and generates a sequence from `from` to `to` in steps of `1` or `-1`. Value `to` will be included if it differs from `from` by an integer up to a numeric fuzz of about `1e-7`. Non-numeric arguments are coerced internally (hence without dispatching methods) to numeric—complex values will have their imaginary parts discarded with a warning.

## Value

For numeric arguments, a numeric vector. This will be of type `integer` if `from` is integer-valued and the result is representable in the R integer type, otherwise of type `"double"` (aka `mode` `"numeric"`).

For factors, an unordered factor with levels labelled as `la:lb` and ordered lexicographically (that is, `lb` varies fastest).

## References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
(for numeric arguments: S does not have `:` for factors.)

`seq` (a generalization of `from:to`).
As an alternative to using `:` for factors, `interaction`.
For `:` used in the formal representation of an interaction, see `formula`.
 ```1 2 3 4 5 6 7``` ```1:4 pi:6 # real 6:pi # integer f1 <- gl(2, 3); f1 f2 <- gl(3, 2); f2 f1:f2 # a factor, the "cross" f1 x f2 ```