This seems very similar to the data.table package. The 'by' argument splits the data.table by that value then executes the j expression within each subset. The package documentation talks about 'subset' and 'with' in some detail. See ?"[.data.table".
dt = data.table(x=1:20, y=rep(1:4,each=5) dt[,sum(x),by="y"] > and x has a variable called grp, what do you get? In data.table that choice is given to the user via the argument 'with' which by default is TRUE meaning you get the x inside dt. "Romain Francois" <romain.franc...@dbmail.com> wrote in message news:4b288645.3010...@dbmail.com... > On 12/16/2009 12:14 AM, Peter Dalgaard wrote: >> Romain Francois wrote: >>> Hello, >>> >>> I very much enjoy "with" and "subset" semantics for data frames and >>> was wondering if we could have something similar with split, basically >>> by evaluating the second argument "with" the data frame : >> >> I seem to recall that this idea was considered and rejected when the >> current split.data.frame was written (10 years ago!). The main reasons >> were that >> >> - it's not really THAT hard to evaluate a single splitting expression >> using with() or eval() > > Sure, this is just about convenience and laziness. > >> - not all applications will have the splitting factor inside the df to >> split ( split(df[-1], df[[1]]) for a simple case) > > this still works > >> - if you need a computed splitting factor, there's a risk of inadvertent >> variable capture. I.e., if you inside a function do >> >> .... >> grp <- ...whatever... >> spl <- split(x, grp) >> .... >> >> and x has a variable called grp, what do you get? > > this is a problem indeed. > > thanks for the reply. > > Romain > > -- > Romain Francois > Professional R Enthusiast > +33(0) 6 28 91 30 30 > http://romainfrancois.blog.free.fr > |- http://tr.im/HlX9 : new package : bibtex > |- http://tr.im/Gq7i : ohloh > `- http://tr.im/FtUu : new package : highlight > ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
