#' The function to impute ordered categorical variables
#'
#' The function uses the proportional odds logistic regression (polr) approach,
#' implemented in \code{mice}.
#' @param y_imp_multi A Vector with the variable to impute.
#' @param X_imp_multi A data.frame with the fixed effects variables.
#' @return A n x 1 matrix.
imp_orderedcat_single <- function(y_imp_multi, X_imp_multi){
categories <- levels(y_imp_multi)
#Initialising the returning vector
y_imp <- as.matrix(y_imp_multi, ncol = 1)
#the missing indactor indicates, which values of y are missing.
missind <- is.na(y_imp_multi)
types <- array(dim = ncol(X_imp_multi))
for(j in 1:length(types)) types[j] <- get_type(X_imp_multi[, j])
categorical <- types == "categorical"
#remove categories with more than 10 observations as the model in the current form
#will cause later numerical probles
too_many_levels <- colnames(X_imp_multi[, categorical, drop = FALSE])[
apply(X_imp_multi[, categorical, drop = FALSE], 2, function(x) nlevels(factor(x))) > 10]
X_imp_multi <- X_imp_multi[, !names(X_imp_multi) %in% too_many_levels, drop = FALSE]
n <- length(y_imp_multi)
lmstart <- stats::lm(stats::rnorm(n) ~ 0 +., data = X_imp_multi)
X_model_matrix_1 <- stats::model.matrix(lmstart)
xnames_1 <- paste("X", 1:ncol(X_model_matrix_1), sep = "")
tmp_1 <- data.frame(y = stats::rnorm(n))
tmp_1[, xnames_1] <- X_model_matrix_1
reg_1 <- stats::lm(y ~ 0 + . , data = tmp_1)
blob <- y_imp_multi
tmp_2 <- data.frame(y = blob)
xnames_2 <- xnames_1[!is.na(stats::coefficients(reg_1))]
tmp_2[, xnames_2] <- X_model_matrix_1[, !is.na(stats::coefficients(reg_1)), drop = FALSE]
everything <- mice::mice(data = tmp_2, m = 1,
method = "polr",
predictorMatrix = (1 - diag(1, ncol(tmp_2))),
visitSequence = (1:ncol(tmp_2))[apply(is.na(tmp_2),2,any)],
post = vector("character", length = ncol(tmp_2)),
defaultMethod = "polr",
maxit = 10,
diagnostics = TRUE,
printFlag = FALSE,
seed = NA,
imputationMethod = NULL,
defaultImputationMethod = NULL,
data.init = NULL)
y_imp[is.na(y_imp_multi),] <- everything$imp[[1]][, 1]
return(y_imp)
}
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