A plot method for GAM objects, which can be used on GLM and LM objects as well. It focuses on terms (main-effects), and produces a suitable plot for terms of different types
# S3 method for Gam
plot(
x,
residuals = NULL,
rugplot = TRUE,
se = FALSE,
scale = 0,
ask = FALSE,
terms = labels.Gam(x),
...
)# S3 method for Gam
preplot(object, newdata, terms = labels.Gam(object), ...)
a plot is produced for each of the terms in the object
x. The function currently knows how to plot all
main-effect functions of one or two predictors. So in particular,
interactions are not plotted. An appropriate x-y is produced to
display each of the terms, adorned with residuals, standard-error
curves, and a rugplot, depending on the choice of options. The
form of the plot is different, depending on whether the x-value
for each plot is numeric, a factor, or a matrix.
When ask=TRUE, rather than produce each plot sequentially,
plot.Gam() displays a menu listing all the terms that can be plotted,
as well as switches for all the options.
A preplot.Gam object is a list of precomputed terms. Each such term
(also a preplot.Gam object) is a list with components x,
y and others---the basic ingredients needed for each term plot. These
are in turn handed to the specialized plotting function gplot(),
which has methods for different classes of the leading x argument. In
particular, a different plot is produced if x is numeric, a category
or factor, a matrix, or a list. Experienced users can extend this range by
creating more gplot() methods for other classes. Graphical
parameters (see par) may also be supplied as arguments to this
function. This function is a method for the generic function plot()
for class "Gam".
It can be invoked by calling plot(x) for an object x of the
appropriate class, or directly by calling plot.Gam(x) regardless of
the class of the object.
a Gam object, or a preplot.Gam object. The
first thing plot.Gam() does is check if x has a
component called preplot; if not, it computes one using
preplot.Gam(). Either way, it is this preplot.Gam
object that is required for plotting a Gam object.
if TRUE, partial deviance residuals are
plotted along with the fitted terms---default is FALSE. If
residuals is a vector with the same length as each fitted
term in x, then these are taken to be the overall
residuals to be used for constructing the partial residuals.
if TRUE (the default), a univariate histogram
or rugplot is displayed along the base of each plot,
showing the occurrence of each x; ties are broken by jittering.
if TRUE, upper and lower pointwise
twice-standard-error curves are included for each plot. The
default is FALSE.
a lower limit for the number of units covered by the
limits on the y for each plot. The default is scale=0,
in which case each plot uses the range of the functions being
plotted to create their ylim. By setting scale to
be the maximum value of diff(ylim) for all the plots, then
all subsequent plots will produced in the same vertical
units. This is essential for comparing the importance of fitted
terms in additive models.
if TRUE, plot.Gam() operates in interactive mode.
subsets of the terms can be selected
Additonal plotting arguments, not all of which will work (like xlim)
same as x
if supplied to preplot.Gam, the preplot object is based on them rather than the original.
Written by Trevor Hastie, following closely the design in the "Generalized Additive Models" chapter (Hastie, 1992) in Chambers and Hastie (1992).
Hastie, T. J. (1992) Generalized additive models. Chapter 7 of Statistical Models in S eds J. M. Chambers and T. J. Hastie, Wadsworth & Brooks/Cole.
Hastie, T. and Tibshirani, R. (1990) Generalized Additive Models. London: Chapman and Hall.
preplot, predict.Gam
data(gam.data)
Gam.object <- gam(y ~ s(x,6) + z,data=gam.data)
plot(Gam.object,se=TRUE)
data(gam.newdata)
preplot(Gam.object,newdata=gam.newdata)
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