## Create 2 two-million length vectors, one character and one factor
animalsChar <- c(rep("giraffe", 1e6), rep("pygmy chimpanzee", 1e6))
animalsFac  <- factor(animalsChar)

## Save them to two ".Rdata" files
charFile <- "char.Rdata"
facFile <-  "fac.Rdata"
save(animalsChar, file = "char.Rdata")
save(animalsFac, file = "fac.Rdata")

## Compare the sizes of the two files
file.info("char.Rdata", "fac.Rdata")["size"]
#             size
# char.Rdata 87390
# fac.Rdata   7921


## Clean up
unlink(c("char.Rdata", "fac.Rdata"))

> x <- rep(c("x","y","z"),1e6)
> print(object.size(x),units="Mb")
22.9 Mb
> print(object.size(factor(x)),units="Mb")
11.4 Mb
> version
               _
platform       x86_64-pc-linux-gnu
arch           x86_64
os             linux-gnu
system         x86_64, linux-gnu
status
major          3
minor          1.3
year           2015
month          03
day            09
svn rev        67962
language       R
version.string R version 3.1.3 (2015-03-09)
nickname       Smooth Sidewalk