Hi r-help-boun...@r-project.org napsal dne 01.03.2010 11:26:40:
> On Mon, 1 Mar 2010 11:02:59 +0100 Karl Ove Hufthammer <k...@huftis.org> > wrote: > > > * What were your biggest misconceptions or > > > stumbling blocks to getting up and running > > > with R? > > > > Also I found it quite confusing that > > One more thing that still trips me up sometimes. '$' works on data > frames but not on matrices (with dimnames/colnames). Even though the two > objects *look* exactly the same, '$' on one of them works while '$' on > the other gives a *very* confusing error message. Example: > > d=head(iris[1:4]) > d2=as.matrix(d) > > d > d2 > > d$Sepal.Width > d2$Sepal.Width > > Some functions output matrices where you would expect them to output > data frames, and then this problem occurs. (Is there a reason why '$' > could/should not be made to 'work' on matrices too?) I understand that 2 dimensional rectangular matrix looks quite similar to data frame however it is only a vector with dimensions. As such it can have items of only one type (numeric, character, ...). And you can easily change dimensions of matrix. matrix<-1:12 dim(matrix) <- c(2,6) matrix dim(matrix) <- c(2,2,3) matrix dim(matrix) <-NULL matrix So rectangular structure of printed matrix is a kind of coincidence only, whereas rectangular structure of data frame is its main feature. Regards Petr > > -- > Karl Ove Hufthammer > > ______________________________________________ > 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. ______________________________________________ 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.
