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+#' Anova method for saem.mmkin objects
+#'
+#' Generate an anova object. The method to calculate the BIC is that from
+#' the saemix package.
+#'
+#' @param object An [saem.mmkin] object
+#' @param ... further such objects
+#' @param method Method for likelihood calculation: "is" (importance sampling),
+#' "lin" (linear approximation), or "gq" (Gaussian quadrature). Passed
+#' to [saemix::logLik.SaemixObject]
+#' @param test Should a likelihood ratio test be performed? If TRUE,
+#' the alternative models are tested against the first model. Should
+#' only be done for nested models.
+#' @param model.names Optional character vector of model names
+#' @importFrom stats anova logLik update
+#' @export
+#' @return an "anova" data frame; the traditional (S3) result of anova()
+anova.saem.mmkin <- function(object, ...,
+ method = c("is", "lin", "gq"), test = FALSE, model.names = NULL)
+{
+ # The following code is heavily inspired by anova.lmer in the lme4 package
+ mCall <- match.call(expand.dots = TRUE)
+ dots <- list(...)
+ method <- match.arg(method)
+
+ is_model <- sapply(dots, is, "saem.mmkin")
+ if (any(is_model)) {
+ mods <- c(list(object), dots[is_model])
+
+ # Ensure same data, ignoring covariates
+ same_data <- sapply(dots[is_model], function(x) {
+ identical(object$data[c("ds", "name", "time", "value")],
+ x$data[c("ds", "name", "time", "value")])
+ })
+ if (!all(same_data)) {
+ stop(sum(!same_data), " objects have not been fitted to the same data")
+ }
+
+ if (is.null(model.names))
+ model.names <- vapply(as.list(mCall)[c(FALSE, TRUE, is_model)], deparse1, "")
+
+ # Sanitize model names
+ if (length(model.names) != length(mods))
+ stop("Model names vector and model list have different lengths")
+
+ if (any(duplicated(model.names)))
+ stop("Duplicate model names are not allowed")
+
+ if (max(nchar(model.names)) > 200) {
+ warning("Model names longer than 200 characters, assigning generic names")
+ model.names <- paste0("MODEL",seq_along(model.names))
+ }
+ names(mods) <- model.names
+
+ llks <- lapply(model.names, function(x) {
+ llk <- try(logLik(mods[[x]], method = method))
+ if (inherits(llk, "try-error"))
+ stop("Could not obtain log likelihood with '", method, "' method for ", x)
+ return(llk)
+ })
+
+ # Order models by increasing degrees of freedom:
+ npar <- vapply(llks, attr, FUN.VALUE=numeric(1), "df")
+ ii <- order(npar)
+ mods <- mods[ii]
+ llks <- llks[ii]
+ npar <- npar[ii]
+
+ # Describe data for the header, as in summary.saem.mmkin
+ header <- paste("Data:", nrow(object$data), "observations of",
+ length(unique(object$data$name)), "variable(s) grouped in",
+ length(unique(object$data$ds)), "datasets\n")
+
+ # Calculate statistics
+ llk <- unlist(llks)
+ chisq <- 2 * pmax(0, c(NA, diff(llk)))
+ dfChisq <- c(NA, diff(npar))
+
+ bic <- function(x, method) {
+ BIC(x$so, method = method)
+ }
+ val <- data.frame(
+ npar = npar,
+ AIC = sapply(llks, AIC),
+ BIC = sapply(mods, bic, method = method), # We use the saemix method here
+ Lik = llk,
+ row.names = names(mods), check.names = FALSE)
+
+ if (test) {
+ testval <- data.frame(
+ Chisq = chisq,
+ Df = dfChisq,
+ "Pr(>Chisq)" = ifelse(dfChisq == 0, NA,
+ pchisq(chisq, dfChisq, lower.tail = FALSE)),
+ row.names = names(mods), check.names = FALSE)
+ val <- cbind(val, testval)
+ }
+ class(val) <- c("anova", class(val))
+ structure(val, heading = c(header))
+ } else {
+ stop("Currently, no anova method is implemented for the case of a single saem.mmkin object")
+ }
+}

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