Timothée, On Jul 4, 2011, at 2:47 AM, Timothée Carayol wrote:
> Hi -- > > It's my first post on this list; as a relatively new user with little > knowledge of R internals, I am a bit intimidated by the depth of some > of the discussions here, so please spare me if I say something > incredibly silly. > > I feel that someone at this point should mention Matthew Dowle's > excellent data.table package > (http://cran.r-project.org/web/packages/data.table/index.html) which > seems to me to address many of the inefficiencies of data.frame. > data.tables have no row names; and operations that only need data from > one or two columns are (I believe) just as quick whether the total > number of columns is 5 or 1000. This results in very quick operations > (and, often, elegant code as well). > I agree that data.table is a very good alternative (for other reasons) that should be promoted more. The only slight snag is that it doesn't help with the issue at hand since it simply does a pass-though for subassignments to data frame's methods and thus suffers from the same problems (in fact there is a rather stark asymmetry in how it handles subsetting vs subassignment - which is a bit surprising [if I read the code correctly you can't use the same indexing in both]). In fact I would propose that it should not do that but handle the simple cases itself more efficiently without unneeded copies. That would make it indeed a very interesting alternative. Cheers, Simon > > On Mon, Jul 4, 2011 at 6:19 AM, ivo welch <ivo.we...@gmail.com> wrote: >> thank you, simon. this was very interesting indeed. I also now >> understand how far out of my depth I am here. >> >> fortunately, as an end user, obviously, *I* now know how to avoid the >> problem. I particularly like the as.list() transformation and back to >> as.data.frame() to speed things up without loss of (much) >> functionality. >> >> >> more broadly, I view the avoidance of individual access through the >> use of apply and vector operations as a mixed "IQ test" and "knowledge >> test" (which I often fail). However, even for the most clever, there >> are also situations where the KISS programming principle makes >> explicit loops still preferable. Personally, I would have preferred >> it if R had, in its standard "statistical data set" data structure, >> foregone the row names feature in exchange for retaining fast direct >> access. R could have reserved its current implementation "with row >> names but slow access" for a less common (possibly pseudo-inheriting) >> data structure. >> >> >> If end users commonly do iterations over a data frame, which I would >> guess to be the case, then the impression of R by (novice) end users >> could be greatly enhanced if the extreme penalties could be eliminated >> or at least flagged. For example, I wonder if modest special internal >> code could store data frames internally and transparently as lists of >> vectors UNTIL a row name is assigned to. Easier and uglier, a simple >> but specific warning message could be issued with a suggestion if >> there is an individual read/write into a data frame ("Warning: data >> frames are much slower than lists of vectors for individual element >> access"). >> >> >> I would also suggest changing the "Introduction to R" 6.3 from "A >> data frame may for many purposes be regarded as a matrix with columns >> possibly of differing modes and attributes. It may be displayed in >> matrix form, and its rows and columns extracted using matrix indexing >> conventions." to "A data frame may for many purposes be regarded as a >> matrix with columns possibly of differing modes and attributes. It may >> be displayed in matrix form, and its rows and columns extracted using >> matrix indexing conventions. However, data frames can be much slower >> than matrices or even lists of vectors (which, like data frames, can >> contain different types of columns) when individual elements need to >> be accessed." Reading about it immediately upon introduction could >> flag the problem in a more visible manner. >> >> >> regards, >> >> /iaw >> >> ______________________________________________ >> R-devel@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel >> > > ______________________________________________ > R-devel@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-devel > > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
