> Your request is reminding me of the analysis of aray functions in Philip S > Abrams dissertation > http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-r-114.pdf > AN APL MACHINE > > The section that starts on page 17 with this paragraph is the one that > immediately applies > > C. The Standard Form for Select Expressions > > In this section the selection operators considered are take, drop, reversal, > transpose, and subscripting by scalars or _J-vectors. Because of the > similarity > among the selection operators, we might expect that an expression consisting > only > of selection operators applied to a single array could be expressed > equivalently in > terms of some simpler set of operators. This expectation is fulfilled in the > standard form for select expressions, to be discussed below.
That's fantastic - thanks for the pointer. One thing I'd like to do with the plyr package is generate a natural (and minimal) set of operators for data frames in a similar way APL did for arrays. Hadley -- Assistant Professor / Dobelman Family Junior Chair Department of Statistics / Rice University http://had.co.nz/ ______________________________________________ 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.