Jessica, thank you for your reply.

Hi Eik,

thank you VERY for your reply and thorough explanation!

I hadn't understood what arrays are and after receiving your mail I read
more on arrays (and data types, modes, classes etc in general) (and
understood more than a few month ago) and understood this problem - and
also the structures in R became a lot clearer.

Thanks again for your help!

Marion

2012/7/19 Eik Vettorazzi <E.Vettorazzi@uke.de>

> Hi Marion,
> as stated in the help file ?apply coerces a data.frame object into an
> array. Since an array has only one type of data, this coercion turns all
> your variables into strings (because this data type can hold all
> information given without loss).
>
> If it happens that your data.frame consists only of numeric variables,
> then this type suffices for the array as well, and things like sum or
> mean can be applied row/columnwise.
>
> btw:
>
> apply(mydataframe,2,function(x)sum(x))
>
> doesn't work either (for the same reason).
>
> Cheers
>
> Am 19.07.2012 11:48, schrieb Marion Wenty:
> > Dear people,
> >
> > I am including an example of a dataframe:
> >
> >
> mydataframe<-data.frame(X=c(1:4),total_bill=c(16.99,10.34,21.01,23.68),tip=c(1.01,1.66,3.50,3.31),sex=c("Male","Male","Male","Female"))
> >
> > When I use the sapply function getting the information about the factors
> > works:
> >
> > sapply(mydataframe,function(x)is.factor(x))
> >
> >          X total_bill        tip        sex
> >      FALSE      FALSE      FALSE       TRUE
> >
> >
> > But if I use the apply function it doesn't work:
> >
> > apply(mydataframe,2,function(x)is.factor(x))
> >
> >          X total_bill        tip        sex
> >      FALSE      FALSE      FALSE      FALSE
> >
> >
> > I don't understand why, because I have used the apply function for
> > dataframes before e.g. using sum(x) instead of is.factor(x) and it did
> work.
> >
> > Could anyone help me with this?
> >
> > Thank you very much for your help in advance!
> >
> > Marion
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > R-help@r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> >
>
>
> --
> Eik Vettorazzi
>
> Department of Medical Biometry and Epidemiology
> University Medical Center Hamburg-Eppendorf
>
> Martinistr. 52
> 20246 Hamburg
>
> T ++49/40/7410-58243
> F ++49/40/7410-57790
>
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