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rgdata

What is the difference between drop.levels(x) in the gdata package and as.factor(as.character(x))?

as question, as I can see the speed is higher for the later method, why use the first one? Thanks.

Solution

  • The two command does quite the same but not exactly, especially when you have the preserve the original order of the factors. In some cases you cannot use: as.factor(as.character(f)). See:

    par(mfrow=c(2,3))
f <- factor(c("D", "B", "C", "K", "A"), levels=c("K", "B", "C", "D"))[2:4]
plot(f, main="Original factor")
f.fc <- as.factor(as.character(f))
plot(f.fc, main="as.factor(as.character(f))")
f.d <- drop.levels(f)
plot(f.d, main="drop.levels(f)")
f.d <- drop.levels(f, reorder=FALSE)
plot(f.d, main="drop.levels(f, reorder=FALSE))")
f.f <- factor(f)
plot(f.f, main="factor(f)")

    alt text

    as.factor(as.character(f)) and drop.levels(f) does the same and they do not preserve the original order of factors, they both re-level the text in ABC order. I you want to preserve the order you can use the reorder=FALSE option in drop.levels().

    This is the default behavior of factor().