On 2017-04-12 14:40, Ulrich Windl wrote:
The last line of the example in droplevels' manual page seems to be
incorrect to me. I think it should read:
"table(droplevels(aq$Month))". Amazingly (I don't understand) both
variants seem to produce the same result (R 3.3.3): ---
The manual says that "The function 'droplevels' is used to drop unused
levels from a 'factor' or, more commonly, from factors in a data frame."
and, as documented, the 'droplevels' generic has methods for objects of
class "data.frame" and "factor". So, your being amazed is a bit
surprising given that 'aq' is a data frame.
Henric Winell
aq <- transform(airquality, Month = factor(Month, labels =
month.abb[5:9])) aq <- subset(aq, Month != "Jul") table(aq$Month)
May Jun Jul Aug Sep 31 30 0 31 30
table(droplevels(aq)$Month)
May Jun Aug Sep 31 30 31 30
table(droplevels(aq$Month))
May Jun Aug Sep 31 30 31 30
--- For the sake of learners, try to keep the examples simple and
useful, even though you experts want to impress the newbees...
Ulrich
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