first function

R/subset.drop.all.R

+##' @title Drop unused levels after subset
+##' @name subset.drop.all
+##'
+##' @description This function is designed to be used in place of
+##'     \code{\link[base]{subset}} when you want to drop off all empty
+##'     levels, of all factor columns in a data frame.
+##'
+##' @param x Object to be subsetted
+##' @param ... further arguments to be passed to or from other methods
+##'
+##' @details This function works exactly the same way as
+##'     \code{\link[base]{subset}} but it will drop off all empty levels
+##'     of all columns that are factors in \code{x}.
+##'
+##' @return An object similar to \code{x} containing just the selected
+##'     rows and columns (for a data frame). Column factors that have
+##'     one or more levels emptied after the subset, will have this
+##'     levels droped off.
+##'
+##' @author Fernando Mayer \email{fernando.mayer@ufpr.br}
+##'
+##' @seealso \code{\link[base]{subset}}
+##'
+##' @export
+subset.drop.all <- function(x, ...){
+    if(!is.data.frame(x)) stop("'x' must be a data.frame")
+    x <- subset(x, ...)
+    factors <- which(sapply(x, class) %in% "factor")
+    for(i in factors){
+        x[,i] <- sapply(x[,i], "[", drop=T)
+    }
+    return(x)
+}