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 2.1.0 Index]