| expand.model.frame {stats} | R Documentation |
Add new variables to a model frame
Description
Evaluates new variables as if they had been part of the formula of the
specified model. This ensures that the same na.action and
subset arguments are applied and allows, for example, x
to be recovered for a model using sin(x) as a predictor.
Usage
expand.model.frame(model, extras,
envir = environment(formula(model)),
na.expand = FALSE)
Arguments
model |
a fitted model |
extras |
one-sided formula or vector of character strings describing new variables to be added |
envir |
an environment to evaluate things in |
na.expand |
logical; see below |
Details
If na.expand = FALSE then NA values in the extra variables
will be passed to the na.action function used in
model. This may result in a shorter data frame (with
na.omit) or an error (with na.fail). If
na.expand = TRUE the returned data frame will have precisely the
same rows as model.frame(model), but the columns corresponding to
the extra variables may contain NA.
Value
A data frame.
See Also
Examples
model <- lm(log(Volume) ~ log(Girth) + log(Height), data = trees)
expand.model.frame(model, ~ Girth) # prints data.frame like
dd <- data.frame(x = 1:5, y = rnorm(5), z = c(1,2,NA,4,5))
model <- glm(y ~ x, data = dd, subset = 1:4, na.action = na.omit)
expand.model.frame(model, "z", na.expand = FALSE) # = default
expand.model.frame(model, "z", na.expand = TRUE)