Nothing
splitMatrix <- function (x, f, drop=FALSE) {
lapply(split(seq_len(nrow(x)), f, drop = drop),
function(ind) x[ind, , drop = FALSE])
}
fixEvent <- function(event)
{
### Convert outcome in clogit model to 0/1 binary coding
if (any(is.na(event)))
stop("Event contains missing values")
if (is.logical(event)) {
status <- is.numeric(event)
}
else if (is.numeric(event)) {
status <- if (max(event) == 2) event - 1 else event
temp <- (status == 0 | status == 1)
if (!all(temp)) {
warning("If outcome is numeric then it must be coded 0/1 or 1/2")
}
}
else if (is.factor(event)) {
if (nlevels(event) != 2)
stop("If outcome is a factor then it must have 2 levels")
status <- event == levels(event)[2]
}
return(as.integer(status))
}
isInformative <- function(Xsplit, ysplit, strata)
{
## Identify which observations are informative in a conditional
## logistic regression.
is.homogeneous <- function(x) { all(x==x[1]) }
y.bad <- sapply(ysplit, is.homogeneous)
X.bad <- sapply(Xsplit, function(x) { all(apply(x, 2, is.homogeneous)) })
is.informative <- vector("list", length(ysplit))
for (i in seq(along=is.informative)) {
canuse <- (!y.bad[i]) && (!X.bad[i])
is.informative[[i]] <- rep(canuse, length(ysplit[[i]]))
}
return(unsplit(is.informative, strata))
}
fitClogit <- function(X, y, offset, strata, init, iter.max, eps, toler.chol)
{
## Safe wrapper around the C function "clogit" that ensures all
## arguments have the correct type and storage mode.
y <- fixEvent(y)
if (!is.matrix(X)) {
X <- as.matrix(X)
}
if (!is.double(X)) {
X <- matrix(as.double(X), nrow(X), ncol(X))
}
if (is.null(offset)) {
offset <- rep(0, nrow(X))
}
offset <- as.double(offset);
## Split into strata
Xsplit <- splitMatrix(X, strata, drop=TRUE)
ysplit <- split(y, strata, drop=TRUE)
osplit <- split(offset, strata, drop=TRUE)
info <- isInformative(Xsplit, ysplit, strata)
if (!any(info)) {
stop("There are no informative observations")
}
ans <- .Call(C_clogit, Xsplit, ysplit, osplit, as.double(init),
as.integer(iter.max), as.double(eps), as.double(toler.chol))
ans$informative <- info
return(ans)
}
clogistic <- function (formula, strata, data, subset, na.action,
init, model = TRUE, x = FALSE, y = TRUE,
contrasts = NULL, iter.max=20, eps=1e-6,
toler.chol = sqrt(.Machine$double.eps))
{
## User interface, edited version of glm
call <- match.call()
if (missing(data))
data <- environment(formula)
mf <- match.call(expand.dots = FALSE)
m <- match(c("formula", "data", "subset",
"na.action", "offset", "strata"), names(mf), 0L)
mf <- mf[c(1, m)]
mf$drop.unused.levels <- TRUE
mf[[1L]] <- as.name("model.frame")
mf <- eval(mf, parent.frame())
mt <- attr(mf, "terms")
Y <- model.response(mf, "any")
if (is.null(Y)) stop("missing outcome")
if (length(dim(Y)) == 1L) {
nm <- rownames(Y)
dim(Y) <- NULL
if (!is.null(nm))
names(Y) <- nm
}
X <- if (!is.empty.model(mt))
model.matrix(mt, mf, contrasts)
else stop("Invalid model matrix")
offset <- as.vector(model.offset(mf))
if (!is.null(offset)) {
if (length(offset) != NROW(Y))
stop(gettextf("number of offsets is %d should equal %d (number of observations)",
length(offset), NROW(Y)), domain = NA)
}
strata <- model.extract(mf, "strata")
if (is.null(strata)) stop("argument 'strata' missing")
contrasts <- attr(X, "contrasts")
if (attr(mt, "intercept") > 0) {
X <- X[,-1, drop=FALSE]
}
if (missing(init))
init <- rep(0, ncol(X))
if (iter.max < 0)
stop("'iter.max' must be non-negative")
if (eps <= 0)
stop("'eps' must be positive")
if (toler.chol <= 0)
stop("'toler.chol' must be positive")
if (eps < toler.chol)
stop("'toler.chol' must be smaller than 'eps'")
fit <- fitClogit(X = X, y = Y, offset = offset, strata=strata, init=init,
toler.chol=toler.chol, eps=eps, iter.max=iter.max)
if (fit$flag <= 0) {
stop("Information matrix is not positive definite")
}
else if (fit$flag == 1000) {
warning("Iteration limit exceeded")
}
nvar <- length(init)
which.sing <- if (fit$flag < nvar) {
diag(fit$var)==0
} else {
rep(FALSE, nvar)
}
fit$coefficients[which.sing] <- NA
fit$flag <- NULL
## Add back in parameter names
cfnames <- colnames(X)
names(fit$coefficients) <- cfnames
dimnames(fit$var) <- list(cfnames, cfnames)
fit$n <- sum(fit$informative)
if (model) {
fit$model <- mf
}
else {
## Without model frame this cannot be interpreted
fit$informative <- NULL
}
fit$na.action <- attr(mf, "na.action")
if (x)
fit$x <- X
if (!y)
fit$y <- NULL
fit <- c(fit, list(call = call, formula = formula, terms = mt,
contrasts = contrasts, xlevels = .getXlevels(mt, mf)))
class(fit) <- c("clogistic")
fit
}
coef.clogistic <- function(object,...) { object$coefficients }
vcov.clogistic <- function(object, ...) { object$var }
print.clogistic <- function (x, digits = max(options()$digits - 4, 3), ...)
{
## Print method for clogistic objects, edited from print.coxph
cat("\nCall: ", deparse(x$call), "\n\n", sep="\n")
savedig <- options(digits = digits)
on.exit(options(savedig))
coef <- coef.clogistic(x)
se <- sqrt(diag(vcov.clogistic(x)))
if (is.null(coef) | is.null(se))
stop("Input is not valid")
coefmat <- cbind(coef, exp(coef), se, coef/se,
signif(1 - pchisq((coef/se)^2, 1), digits - 1))
dimnames(coefmat) <- list(names(coef),
c("coef", "exp(coef)", "se(coef)", "z", "p"))
cat("\n")
prmatrix(coefmat)
logtest <- -2 * (x$loglik[1] - x$loglik[2])
if (is.null(x$df))
df <- sum(!is.na(coef))
else df <- round(sum(x$df), 2)
cat("\n")
cat("Likelihood ratio test=", format(round(logtest, 2)),
" on ", df, " df,", " p=", format(1 - pchisq(logtest, df)),
", n=", x$n, sep = "")
cat("\n")
invisible()
}
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