On 03-May-10 11:09:43, adrien Penac wrote: > Hello, > I can't find how to get de column name from a data.frame dollar > reference. > > To make it simple, I'd like to obtain "Bar" from a "foo$Bar" notation. > I've tried col.names(foo$Bar), names(foo$Bar) and so on without sucess. > > Regards > Blaise
You cannot expect to! The reason is that foo$Bar is the object which is stored in list/dataframe foo *under* the name "Bar". "Bar" is the index, within foo, of that object. That object may be something that has a "names" attribute (such as a matrix with column names), and this it what would be returned by anything like names(foo$Bar); there is no reason to expect that such names should have any relationship with "Bar". However, I have to ask why you want to find the solution to such a question. In any code which has already extracted foo$Bar from foo, that code has done so by constructing the expression "foo$Bar", and so the code already knows the value "Bar" -- so look for it in the code! A possible exception to that secario is where you want to find out the name of a list/dataframe component in a particular position -- for example, you may want the name under which the 3rd compenent is indexed. For example: foo<-list(Bar1=1,Bar2=2,Bar3=3,Bar4=4) names(foo) # [1] "Bar1" "Bar2" "Bar3" "Bar4" names(foo)[3] # [1] "Bar3" Hoping this helps; if not, then more information is needed about why you are asking the question! Ted. -------------------------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861 Date: 03-May-10 Time: 12:36:35 ------------------------------ XFMail ------------------------------ ______________________________________________ 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.
