update: Update and Re-fit a Model Call

Description

update will update and (by default) re-fit a model. It does this by extracting the call stored in the object, updating the call and (by default) evaluating that call. Sometimes it is useful to call update with only one argument, for example if the data frame has been corrected.

“Extracting the call” in update() and similar functions uses getCall() which itself is a (S3) generic function with a default method that simply gets x$call.

Because of this, update() will often work (via its default method) on new model classes, either automatically, or by providing a simple getCall() method for that class.

Usage

update(object, …)
# S3 method for default
update(object, formula., …, evaluate = TRUE)
getCall(x, …)

Arguments

object, x

An existing fit from a model function such as lm, glm and many others.

formula.

Changes to the formula -- see update.formula for details.

…

Additional arguments to the call, or arguments with changed values. Use name = NULL to remove the argument name.

evaluate

If true evaluate the new call else return the call.

Value

If evaluate = TRUE the fitted object, otherwise the updated call.

References

Chambers, J. M. (1992) Linear models. Chapter 4 of Statistical Models in S eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.

Examples

Run this code

# NOT RUN {
oldcon <- options(contrasts = c("contr.treatment", "contr.poly"))
## Annette Dobson (1990) "An Introduction to Generalized Linear Models".
## Page 9: Plant Weight Data.
ctl <- c(4.17,5.58,5.18,6.11,4.50,4.61,5.17,4.53,5.33,5.14)
trt <- c(4.81,4.17,4.41,3.59,5.87,3.83,6.03,4.89,4.32,4.69)
group <- gl(2, 10, 20, labels = c("Ctl", "Trt"))
weight <- c(ctl, trt)
lm.D9 <- lm(weight ~ group)
lm.D9
summary(lm.D90 <- update(lm.D9, . ~ . - 1))
options(contrasts = c("contr.helmert", "contr.poly"))
update(lm.D9)
getCall(lm.D90)  # "through the origin"

options(oldcon)
# }