Nothing
## Returns a factor from one variable or a list of variable
## some code taken from the tapply function
group <- function (INDEX, factor=TRUE) {
if (!is.factor(INDEX)) {
if (!is.list(INDEX)) { INDEX <- list(INDEX) }
il <- sapply(INDEX, length)
if (min(il)!=max(il)) {
stop(" [!] all factors must have the same length")
}
if (factor) {
group <- rep("", length(INDEX[[1]]))
for (i in seq_along(INDEX)) {
index <- as.factor(INDEX[[i]])
group <- paste(group, index)
group[is.na(index)] <- NA
}
group <- as.factor(group)
}
else {
## fromt apply
nI <- length(INDEX)
namelist <- vector("list", nI)
names(namelist) <- names(INDEX)
extent <- integer(nI)
one <- 1L
group <- rep.int(one, length(INDEX[[1]]))
ngroup <- one
for (i in seq_along(INDEX)) {
index <- as.factor(INDEX[[i]])
namelist[[i]] <- levels(index)
extent[i] <- nlevels(index)
group <- group + ngroup * (as.integer(index) - one)
ngroup <- ngroup * nlevels(index)
}
}
} else {
## Eliminate the unused levels
uf <- unique(INDEX)
fl <- levels(INDEX)[levels(INDEX) %in% uf]
group <- factor(INDEX, levels=fl)
}
return(group)
}
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