interaction {base} | R Documentation |

## Compute Factor Interactions

### Description

`interaction`

computes a factor which represents the interaction
of the given factors. The result of `interaction`

is always unordered.

### Usage

interaction(..., drop = FALSE, sep = ".")

### Arguments

`...` |
the factors for which interaction is to be computed, or a
single list giving those factors. |

`drop` |
if `drop` is `TRUE` , empty factor levels
are dropped from the result. The default is to retain all
factor levels. |

`sep` |
string to construct the new level labels by joining the
constituent ones. |

### Value

A factor which represents the interaction of the given factors.
The levels are labelled as the levels of the individual factors joined
by `sep`

, i.e. `.`

by default.

### References

Chambers, J. M. and Hastie, T. J. (1992)
*Statistical Models in S*.
Wadsworth & Brooks/Cole.

### See Also

`factor`

; `:`

where `f:g`

is the same as
`interaction(f,g, sep=":")`

when `f`

and `g`

are factors.

### Examples

a <- gl(2, 4, 8)
b <- gl(2, 2, 8, label = c("ctrl", "treat"))
s <- gl(2, 1, 8, label = c("M", "F"))
interaction(a, b)
interaction(a, b, s, sep = ":")

[Package

*base* version 2.2.1

Index]