coef.seqModel {robustHD}

Extract coefficients from a sequence of regression models

Description

Extract coefficients from a sequence of regression models, such as submodels along a robust or groupwise least angle regression sequence, or sparse least trimmed squares regression models for a grid of values for the penalty parameter.

Usage

## S3 method for class 'seqModel'
coef(object, s = NA, zeros = TRUE, drop = !is.null(s), ...)

## S3 method for class 'tslars'
coef(object, p, ...)

## S3 method for class 'perrySeqModel'
coef(object, ...)

## S3 method for class 'sparseLTS'
coef(
  object,
  s = NA,
  fit = c("reweighted", "raw", "both"),
  zeros = TRUE,
  drop = !is.null(s),
  ...
)

Arguments

object

the model fit from which to extract coefficients.

s

for the "seqModel" method, an integer vector giving the steps of the submodels for which to extract coefficients (the default is to use the optimal submodel). For the "sparseLTS" method, an integer vector giving the indices of the models for which to extract coefficients. If fit is "both", this can be a list with two components, with the first component giving the indices of the reweighted fits and the second the indices of the raw fits. The default is to use the optimal model for each of the requested estimators. Note that the optimal models may not correspond to the same value of the penalty parameter for the reweighted and the raw estimator.

zeros

a logical indicating whether to keep zero coefficients (TRUE, the default) or to omit them (FALSE).

drop

a logical indicating whether to reduce the dimension to a vector in case of only one submodel.

...

for the "tslars" method, additional arguments to be passed down to the "seqModel" method. For the other methods, additional arguments are currently ignored.

p

an integer giving the lag length for which to extract coefficients (the default is to use the optimal lag length).

fit

a character string specifying which coefficients to extract. Possible values are "reweighted" (the default) for the coefficients from the reweighted estimator, "raw" for the coefficients from the raw estimator, or "both" for the coefficients from both estimators.

Value

A numeric vector or matrix containing the requested regression coefficients.

Author(s)

Andreas Alfons

See Also

coef, rlars, grplars, rgrplars, tslarsP, rtslarsP, tslars, rtslars, sparseLTS

Examples

## generate data
# example is not high-dimensional to keep computation time low
library("mvtnorm")
set.seed(1234)  # for reproducibility
n <- 100  # number of observations
p <- 25   # number of variables
beta <- rep.int(c(1, 0), c(5, p-5))  # coefficients
sigma <- 0.5      # controls signal-to-noise ratio
epsilon <- 0.1    # contamination level
Sigma <- 0.5^t(sapply(1:p, function(i, j) abs(i-j), 1:p))
x <- rmvnorm(n, sigma=Sigma)    # predictor matrix
e <- rnorm(n)                   # error terms
i <- 1:ceiling(epsilon*n)       # observations to be contaminated
e[i] <- e[i] + 5                # vertical outliers
y <- c(x %*% beta + sigma * e)  # response
x[i,] <- x[i,] + 5              # bad leverage points


## robust LARS
# fit model
fitRlars <- rlars(x, y, sMax = 10)
# extract coefficients
coef(fitRlars, zeros = FALSE)
coef(fitRlars, s = 1:5, zeros = FALSE)


## sparse LTS over a grid of values for lambda
# fit model
frac <- seq(0.2, 0.05, by = -0.05)
fitSparseLTS <- sparseLTS(x, y, lambda = frac, mode = "fraction")
# extract coefficients
coef(fitSparseLTS, zeros = FALSE)
coef(fitSparseLTS, fit = "both", zeros = FALSE)
coef(fitSparseLTS, s = NULL, zeros = FALSE)
coef(fitSparseLTS, fit = "both", s = NULL, zeros = FALSE)