[Rd] "table(droplevels(aq)$Month)" in manual page of droplevels

[Henric Winell]

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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