update.formula {stats} | R Documentation |
update.formula
is used to update model formulae.
This typically involves adding or dropping terms,
but updates can be more general.
## S3 method for class 'formula' update(old, new, ...)
old |
a model formula to be updated. |
new |
a formula giving a template which specifies how to update. |
... |
further arguments passed to or from other methods. |
Either or both of old
and new
can be objects such as
length-one character vectors which can be coerced to a formula via
as.formula
.
The function works by first identifying the left-hand side
and right-hand side of the old
formula.
It then examines the new
formula and substitutes
the lhs of the old
formula for any occurrence
of ‘.’ on the left of new
, and substitutes
the rhs of the old
formula for any occurrence
of ‘.’ on the right of new
. The result is then
simplified via terms.formula(simplify = TRUE)
.
The updated formula is returned. The environment of the result is
that of old
.
update(y ~ x, ~ . + x2) #> y ~ x + x2 update(y ~ x, log(.) ~ . ) #> log(y) ~ x