interaction {base} | R Documentation |
interaction
computes a factor which represents the interaction
of the given factors. The result of interaction
is always unordered.
interaction(..., drop = FALSE, sep = ".")
... |
the factors for which interaction is to be computed, or a single list giving those factors. |
drop |
if drop is TRUE , unused 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. |
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.
As from R 2.4.0 the levels are ordered so the level of the first
factor varies fastest, then the second and so on. This is the reverse
of lexicographic ordering.
Chambers, J. M. and Hastie, T. J. (1992) Statistical Models in S. Wadsworth & Brooks/Cole.
factor
; :
where f:g
is the same as
interaction(f,g, sep=":")
when f
and g
are factors.
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 = ":")