Hi, If you want to take advantage of Josh's example below (using an S4 subclass of data.frame), perhaps you might be interested in taking advantage of the multitude of useful objects/classes defined in the bioconductor IRanges package:
http://www.bioconductor.org/packages/release/bioc/html/IRanges.html It has no other bioconductor dependencies, so it's a "slim" install, in that respect. It defines a DataFrame class which keeps "metadata" around with as you subset/index/etc. it, eg: R> library(IRanges) R> DF <- DataFrame(a=1:10, b=letters[1:10]) R> metadata(DF) <- list(units=list(a=NA, b='inches')) R> sub.1 <- subset(DF, a %% 2 == 0) R> sub.1 DataFrame with 5 rows and 2 columns a b <integer> <character> 1 2 b 2 4 d 3 6 f 4 8 h 5 10 j R> metadata(sub.1) $units $units$a [1] NA $units$b [1] "inches" (although I noticed that transform,DataFrame isn't defined actually ...) Anyway, HTH. -steve On Mon, Oct 3, 2011 at 11:15 AM, Joshua Wiley <jwiley.ps...@gmail.com> wrote: > Hi Bruno, > > It sounds like what you want is really a separate class, one that has > stores information about units for each variable. This is far from an > elegant example, but depending on your situation may be useful. I > create a new class inheriting from the data frame class. This is > likely fraught with problems because a formal S4 class is inheriting > from an informal S3. Then a data frame can be stored in the .Data > slot (special---I did not make it), but character data can also be > stored in the units slot (which I did define). You could get fancier > imposing constraints that the length of units be equal to the number > of columns in the data frame or the like. S3 methods for data frames > should still mostly work, but you also have the ability to access the > new units slot. You could define special S4 methods to do the > extraction then, if you wanted, so that your ultimate syntax to get > the units of a particular variable would be shorter. > > setOldClass("data.frame") > > setClass("mydf", representation(units = "character"), > contains = "data.frame", S3methods = TRUE) > > tmp <- new("mydf") > > tmp@.Data <- mtcars > tmp@row.names <- rownames(mtcars) > tmp@units <- c("x", "y") > > ## data frameish > colMeans(tmp) > tmp + 10 > > # but > tmp@units > > Cheers, > > Josh > > N.B. I've read once and skimmeda gain Chambers' book, but I still do > not have a solid grasp on S4 so I may have made some fundamental > blunder in the example. > > > > On Mon, Oct 3, 2011 at 7:35 AM, bruno Piguet <bruno.pig...@gmail.com> wrote: >> Dear all, >> >> I'd like to have a dataframe store information about the units of >> the data it contains. >> >> You'll find below a minimal exemple of the way I do, so far. I add a >> "units" attribute to the dataframe. But I dont' like the long syntax >> needed to access to the unit of a given variable (namely, something >> like : >> var_unit <- attr(my_frame, "units")[[match(var_name, attr(my_frame, >> "names"))]] >> >> Can anybody point me to a better solution ? >> >> Thanks in advance, >> >> Bruno. >> >> >> # Dataframe creation >> x <- c(1:10) >> y <- c(11:20) >> z <- c(101:110) >> my_frame <- data.frame(x, y, z) >> attr(my_frame, "units") <- c("x_unit", "y_unit") >> >> # >> # later on, using dataframe >> for (var_name in c("x", "y")) { >> idx <- match(var_name, attr(my_frame, "names")) >> var_unit <- attr(my_frame, "units")[[idx]] >> print (paste("max ", var_name, ": ", max(my_frame[[var_name]]), var_unit)) >> } >> >> ______________________________________________ >> 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. >> > > > > -- > Joshua Wiley > Ph.D. Student, Health Psychology > Programmer Analyst II, ATS Statistical Consulting Group > University of California, Los Angeles > https://joshuawiley.com/ > > ______________________________________________ > 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. > -- Steve Lianoglou Graduate Student: Computational Systems Biology | Memorial Sloan-Kettering Cancer Center | Weill Medical College of Cornell University Contact Info: http://cbio.mskcc.org/~lianos/contact ______________________________________________ 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.
