Hi everybody,
Is there a particular reason, why this code does not work as intended:
z <- factor(LETTERS[1:3], ordered = TRUE)
u <- 4:6
min(z[u > 4])
Error in Summary.factor(2:3, na.rm = FALSE) :
min not meaningful for factors
I agree that min is indeed not meaningful for not ordered factors, but
it makes sense for ordered factors. Especially since
z[3] < z[2]
sort(z)
_ARE_ defined and work as expected. Of course I can do something like
sort(z[u>4])[1]
but this does not enhance readability of my code. Thus, I overloaded
Summary.ordered as follows:
Summary.ordered <- function(..., na.rm) {
ok <- switch(.Generic, max = , min = , range = TRUE, FALSE)
if (!ok) {
warning(sprintf("'%s' is not meaningful for ordered factors",
.Generic))
return(NA)
}
args <- list(...)
level.list <- lapply(args, levels)
level.set <- Reduce(union, level.list)
if (!all(sapply(args, is.ordered)) || !all(sapply(level.list,
identical, y = level.set))) {
stop(sprintf("'%s' is only meaningful for ordered factors if all
arguments are ordered factors with the same level sets",
.Generic))
}
codes <- lapply(args, as.integer)
ind <- do.call(.Generic, c(codes, na.rm = na.rm))
factor(level.set[ind], levels = level.set, ordered = TRUE)
}
Any comments appreciated.
BR,
Thorn
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