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 ______________________________________________ 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.
