cv.modList {cv}

Cross-Validate Several Models Fit to the Same Data

Description

A cv() method for an object of class "modlist", created by the models() function. This cv() method simplifies the process of cross-validating several models on the same set of CV folds and may also be used for recursive CV, where CV is used to select one from among several models. models() performs some "sanity" checks, warning if the models are of different classes, and reporting an error if they are fit to apparently different data sets or different response variables.

Usage

## S3 method for class 'modList'
cv(
  model,
  data,
  criterion = mse,
  k,
  reps = 1L,
  seed,
  quietly = TRUE,
  recursive = FALSE,
  ...
)

models(...)

## S3 method for class 'cvModList'
print(x, ...)

## S3 method for class 'cvModList'
plot(
  x,
  y,
  spread = c("range", "sd"),
  confint = TRUE,
  xlab = "",
  ylab,
  main,
  axis.args = list(labels = names(x), las = 3L),
  col = palette()[2L],
  lwd = 2L,
  grid = TRUE,
  ...
)

## S3 method for class 'cvModList'
as.data.frame(x, row.names = NULL, optional = TRUE, ...)

Arguments

model

a list of regression model objects, created by models().

data

(required) the data set to which the models were fit.

criterion

the CV criterion ("cost" or lack-of-fit) function, defaults to mse.

k

the number of CV folds; may be omitted, in which case the value will depend on the default for the cv() method invoked for the individual models.

reps

number of replications of CV for each model (default is 1).

seed

(optional) seed for R's pseudo-random-number generator, to be used to create the same set of CV folds for all of the models; if omitted, a seed will be randomly generated and saved. Not used for leave-one-out CV.

quietly

if TRUE (the default), simple messages (for example about the value to which the random-number generator seed is set), but not warnings or errors, are suppressed.

recursive

if TRUE (the default is FALSE), cross-validation is performed recursively to select a "best" model deleting each fold in turn by calculating the CV estimate of the criterion for the remaining folds; this is equivalent to employing the selectModelList() model-selection procedure.

...

for cv.modList(), additional arguments to be passed to the cv() method applied to each model.

For models(), two or more competing models fit to the the same data; the several models may be named.

For the print() method, arguments to be passed to the print() method for the individual model cross-validations.

For the plot() method, arguments to be passed to the base plot() function.

x

an object of class "cvModList" to be printed or plotted.

y

the name of the element in each "cv" object to be plotted; defaults to "adj CV crit", if it exists, or to "CV crit".

spread

if "range", the default, show the range of CV criteria for each model along with their average; if "sd", show the average plus or minus 1 standard deviation.

confint

if TRUE (the default) and if confidence intervals are in any of the "cv" objects, then plot the confidence intervals around the CV criteria.

xlab

label for the x-axis (defaults to blank).

ylab

label for the y-axis (if missing, a label is constructed).

main

main title for the graph (if missing, a label is constructed).

axis.args

a list of arguments for the axis() function, used to draw the horizontal axis. In addition to the axis arguments given explicitly, side=1 (the horizontal axis) and at=seq(along=x) (i.e., 1 to the number of models) are used and can't be modified.

col

color for the line and points, defaults to the second element of the color palette; see palette().

lwd

line width for the line (defaults to 2).

grid

if TRUE (the default), include grid lines on the graph.

row.names

optional row names for the result, defaults to NULL.

optional

to match the as.data.frame() generic function; if FALSE (the default is TRUE), then the names of the columns of the returned data frame, including the names of coefficients, are coerced to syntactically correct names.

Value

models() returns a "modList" object, the cv() method for which returns a "cvModList" object, or, when recursive=TRUE, an object of class c("cvSelect", "cv").

Functions

• cv(modList): cv() method for "modList" objects.

• models(): create a list of models.

• print(cvModList): print() method for "cvModList" objects.

• plot(cvModList): plot() method for "cvModList" objects.

• as.data.frame(cvModList): as.data.frame() method for "cvModList" objects.

See Also

cv, cv.merMod, selectModelList.

Examples

data("Duncan", package="carData")
m1 <- lm(prestige ~ income + education, data=Duncan)
m2 <- lm(prestige ~ income + education + type, data=Duncan)
m3 <- lm(prestige ~ (income + education)*type, data=Duncan)
(cv.models <- cv(models(m1=m1, m2=m2, m3=m3),
                 data=Duncan, seed=7949, reps=5))
D.cv.models <- as.data.frame(cv.models)
head(D.cv.models)
summary(D.cv.models, criterion ~ model + rep, include="folds")
plot(cv.models)
(cv.models.ci <- cv(models(m1=m1, m2=m2, m3=m3),
                    data=Duncan, seed=5962, confint=TRUE, level=0.50))
                 # nb: n too small for accurate CIs
plot(cv.models.ci)
(cv.models.recursive <- cv(models(m1=m1, m2=m2, m3=m3),
                           data=Duncan, seed=5962,
                           recursive=TRUE, save.model=TRUE))
cv.models.recursive$selected.model