[Rd] order(x, y, decreasing = c(FALSE, TRUE)) - how / elegantly?

Martin Maechler maechler at stat.math.ethz.ch
Thu Aug 21 20:12:30 CEST 2008


The simplest, probably fastest and most elegant solution of
course is

       order(x, -y)

......  if only I would have biked home earlier, today,...
	I'm sure I would have save much of my time....


>>>>> "MM" == Martin Maechler <maechler at stat.math.ethz.ch>
>>>>>     on Thu, 21 Aug 2008 19:41:51 +0200 writes:

    MM> I've found the need to compute a version of order(x,y)
    MM> where I want the sort order for *increasing* x and
    MM> *decresing* y ...

    MM> something we could imagine could be provided in the
    MM> future as

    MM>   order(x,y, decreasing = c(FALSE, TRUE))

    MM> i.e., using a 'vectorized' decreasing argument.  {No,
    MM> I'm not volunteering right now!}

    MM> I've found the following R-level solution and like to
    MM> quiz you for more elegant / faster solutions {but I am
    MM> not really interested in replacing order(x) by
    MM> sort.list(x, method="quick") and similar things; one
    MM> thing to consider *is* using an 'na.last = . '
    MM> correctly, and I haven't had the need for that and so
    MM> not bothered to "do it"}

    MM> ## Here's a script with my version and a small example
    MM> ## (if you want speed comparisons, use larger examples)
    MM> :

    MM> orderXuYd <- function(x,y) { ## Purpose: order(x,y): x
    MM> up, y down ##
    MM> ----------------------------------------------------------------------
    MM> ## Arguments: x,y: vectors of the same length ##
    MM> ----------------------------------------------------------------------
    MM> ## Author: Martin Maechler, Date: 21 Aug 2008

    MM>     ix <- order(x) xx <- x[ix] iy <- tapply(y[ix], xx,
    MM> order, decreasing = TRUE) ## Note: 'SIMPLIFY',
    MM> 'USE.NAMES', 'use.names' are just for efficiency:
    MM> unlist(mapply(`[`, split(ix,xx), iy, SIMPLIFY = FALSE,
    MM> USE.NAMES = FALSE), use.names = FALSE) }

    MM> x <- c(1, 1, 2, 0, 0, 2, 1, 2, 2, 0, 2) y <- c(27, 21,
    MM> 45, 11, 13, 58, 35, 74, 95, 16, 122) ii <-
    MM> orderXuYd(x,y) ## yes, this is it : cbind(ii=ii,
    MM> x=x[ii],y=y[ii])

    MM> ------------------

    MM> Yes, the real reason this goes to R-devel is that it
    MM> might be neat to provide this (well, its generalization)
    MM> via an enhanced order() function.

    MM> Martin Maechler, ETH Zurich

    MM> PS: I will be basically offline all day tomorrow, so
    MM> don't expect my reactions to your ideas quickly

    MM> ______________________________________________
    MM> R-devel at r-project.org mailing list
    MM> https://stat.ethz.ch/mailman/listinfo/r-devel

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