Dear List,

When I subset a data.frame, the levels are not re-adjusted (see
example). Why is this? Am I missing out on some basic stuff here?

Thanks
Ulrik


> m <- data.frame(gender = c("M", "M","F"), ht = c(172, 186.5, 165), wt = c(91,99, 74))
> dim(m)
[1] 3 3

> levels(m$gender)
[1] "F" "M"

> s <- subset(m, m$gender == "M")
> dim(s)
[1] 2 3

> levels(s$gender)
[1] "F" "M"

> cat <- sapply(s, is.factor); s[cat] <- lapply(s[cat], factor)
> dim(s)
[1] 2 3

> levels(s$gender)
[1] "M"

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