On Thu, 30 Mar 2006, Patrick Burns wrote: > I haven't been following all of this thread, but > it reminds me of a bug that was in S-PLUS not > too long ago where dimnames could sometimes > be numeric. This caused some problems that > were very hard to track down because there were > no visual clues of what was really wrong. > > I've been pleased not to encounter that in R and > hope it continues.
Yes, the C-level assignment code ensures that what is assigned is character or NULL (even if you set the attribute rather than use dimnames<-). > > Patrick Burns > [EMAIL PROTECTED] > +44 (0)20 8525 0696 > http://www.burns-stat.com > (home of S Poetry and "A Guide for the Unwilling S User") > > Prof Brian Ripley wrote: > >> Looking at the code it occurs to me that there is another case you have >> not considered, namely dimnames(). >> >> rownames<- and colnames<- are just wrappers for dimnames<-, so consistency >> does mean that all three should behave the same. >> >> For arrays (including matrices), dimnames<- is primitive. It coerces >> factors to character, and says in the C code >> >> /* if (isObject(val1)) dispatch on as.character.foo, but we don't >> have the context at this point to do so */ >> >> so someone considered this before now. >> >> For data frames, dimnames<-.data.frame is used. That calls row.names<- >> and names<-, and the first has a data.frame method. Only the row.names<- >> method is documented to coerce its value to character, and I think it _is_ >> all quite consistent. The basic rule is that all these functions coerce >> for data frames, and none do for arrays. >> >> However, there was a problematic assumption in the row.names<-.data.frame >> and dimnames<-.data.frame methods, which tested the length of 'value' >> before coercion. That sounds reasonable, but in unusual cases such as >> POSIXlt, coercion changes the length, and I have swapped the lines around. >> >> What you expected was that dimnames<-() would coerce to character, >> although I can find no support for that expectation in the documentation. >> If it were not a primitive function that would be easy to achieve, but as >> it is, it would need an expert in the internal code to change. There is >> also the risk of inconsistency, since as the comment says, the C code is >> used in places where the context is not known. I think this is probably >> best left alone. >> >> >> On Wed, 29 Mar 2006, Prof Brian Ripley wrote: >> >> >> >>> Yet again, this is the wrong list for suggesting changes to R. Please do >>> use >>> R-devel for that purpose (and I have moved this). >>> >>> If this bothers you (it all works as documented, so why not use it as >>> documented?), please supply a suitable patch to the current R-devel sources >>> and it will be considered. >>> >>> And BTW, row.names is the canonical accessor function for data frames, >>> and its 'value' argument is documented differently from that for rownames >>> for >>> an array. Cf: >>> >>> Details: >>> >>> The extractor functions try to do something sensible for any >>> matrix-like object 'x'. If the object has 'dimnames' the first >>> component is used as the row names, and the second component (if >>> any) is used for the col names. For a data frame, 'rownames' and >>> 'colnames' are equivalent to 'row.names' and 'names' respectively. >>> >>> Note: >>> >>> 'row.names' is similar to 'rownames' for arrays, and it has a >>> method that calls 'rownames' for an array argument. >>> >>> I am not sure why R decided to add rownames for the same purpose as >>> row.names: eventually they were made equivalent. >>> >>> >>> On Tue, 21 Mar 2006, Erich Neuwirth wrote: >>> >>> >>> >>>> I noticed something surprising (in R 2.2.1 on WinXP) >>>> According to the documentation, rownames and colnames are character >>>> vectors. >>>> Assigning a vector of class POSIXct or POSIXlt as rownames or colnames >>>> therefore is not strictly according to the rules. >>>> In some cases, R performs a reasonable typecast, but in some other cases >>>> where the same typecast also would be possible, it does not. >>>> >>>> Assigning a vector of class POSIXct to the rownames or names of a >>>> dataframe creates a reasonable string representation of the dates (and >>>> possibly times). >>>> Assigning such a vector to the rownames or colnames of a matrix produces >>>> rownames or colnames consisting of the integer representation of the >>>> date-time value. >>>> Trying to assign a vector of class POSIXlt in all cases >>>> (dataframes and matrices, rownames, colnames, names) >>>> produces an error. >>>> >>>> Demonstration code is given below. >>>> >>>> This is somewhat inconsistent. >>>> Perhaps a reasonable solution could be that the typecast >>>> used for POSIXct and dataframes is used in all the other cases also. >>>> >>>> Code: >>>> >>>> mymat<-matrix(1:4,nrow=2,ncol=2) >>>> mydf<-data.frame(mymat) >>>> mydates<-as.POSIXct(c("2001-1-24","2005-12-25")) >>>> >>>> rownames(mydf)<-mydates >>>> names(mydf)<-mydates >>>> rownames(mymat)<-mydates >>>> colnames(mymat)<-mydates >>>> >>>> print(deparse(mydates)) >>>> print(deparse(rownames(mydf))) >>>> print(deparse(names(mydf))) >>>> print(deparse(rownames(mymat))) >>>> print(deparse(colnames(mymat))) >>>> >>>> mydates1<-as.POSIXlt(mydates) >>>> >>>> # the following lines will not work and >>>> # produce errors >>>> >>>> rownames(mydf)<-mydates1 >>>> names(mydf)<-mydates1 >>>> rownames(mymat)<-mydates1 >>>> colnames(mymat)<-mydates1 >>>> >>>> >>>> >>>> >>>> >>> >>> >> >> >> > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > > -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
