On 01-Mar-10 12:07:52, Karl Ove Hufthammer wrote: > On Mon, 01 Mar 2010 06:37:30 -0500 Duncan Murdoch > <murd...@stats.uwo.ca> > wrote: >> > 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?) >> > >> The reason for the difference is that data.frames are lists organized >> into columns (so the $ handling comes from the list, where it means >> "extract the component") whereas a matrix is a single vector displayed >> in columns. > > Sure, I know that. But is there are reason why the '$' can't be > overloaded to handle the extraction, as a *convenience* to the user? > After all, it *is* possible to extract columns by name from matrices > too (e.g., using d[,"Sepal.Width"]). > > A similar type of overloading is used in the 'sp' class functions, > where you can basically treat a 'SpatialPointsDataFrame', a > 'SpatialLinesDataFrame' or a 'SpatialPolygonsDataFrame' as a data > frame, > with '$colname' indexing and '[' subsetting, even though the > *internals* > of the objects have a completely different (and very complex) > structure. > But as a convenience to the user, you don't need to bother with the > internals, and can handle the object *as if* it were a data frame. It's > a very comfortable way of working. > > -- > Karl Ove Hufthammer
I'm not sure that "SpatialPointsDataFrame" is a dataframe (despite the name)! Is it not simply a list? In which case, using "$" is what you have to do to get at its components. Ted. -------------------------------------------------------------------- E-Mail: (Ted Harding) <ted.hard...@manchester.ac.uk> Fax-to-email: +44 (0)870 094 0861 Date: 01-Mar-10 Time: 12:25:17 ------------------------------ 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.
