variablesinformula(x)
returns a character vector of the names
of all variables which appear in the formula x
.
termsinformula(x)
returns a character vector of all
terms in the formula x
(after expansion of interaction terms).
offsetsinformula(x)
returns a character vector of all
offset terms in the formula.
rhs.of.formula(x)
returns the right-hand side of the formula
as another formula (that is, it removes the left-hand side) provided
tilde=TRUE
(the default). If tilde=FALSE
, then the
right-hand side is returned as a language object.
lhs.of.formula(x)
returns the left-hand side of the formula
as a symbol or language object, or NULL
if the formula has no
left-hand side.
lhs.of.formula(x) <- value
and rhs.of.formula(x) <- value
change the formula x
by replacing the left or right hand side
of the formula by value
.
can.be.formula(x)
returns TRUE
if x
is a formula
or a character string that can be parsed as a formula, and returns
FALSE
otherwise.
identical.formulae(x,y)
returns TRUE
if x
and
y
are identical formulae (ignoring their environments).