Random Factors
DESCRIPTION:
States or changes whether or not a factor is considered random by the varcomp function.
USAGE: 
is.random(object)
is.random(object) <- value
REQUIRED ARGUMENTS:
object:
a factor or a data frame.
OPTIONAL ARGUMENTS:
value:
a logical vector.
VALUE:
a logical vector stating whether or not each factor contained in object is random or fixed.
SIDE EFFECTS:
the assignment form changes the status of factors in object. If value is shorter than than the number of factors in object, then value is replicated.
DETAILS:
The is.random function is generic with a method for "data.frame" and a method for "factor".

A factor is random if it is of class "ranfact" which inherits from "factor".

SEE ALSO:
varcomp , factor .
EXAMPLES: 
is.random(guayule[,c("reps","flats")]) <- T
is.random(guayule)