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

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Thu, 21 Aug 2008 19:27:51 +0100 (BST)

On Thu, 21 Aug 2008, Martin Maechler wrote:

> Duh!!
>
> The simplest, probably fastest and most elegant solution of
> course is
>
> order(x, -y)

Only for numeric x. As Martin knows, I am working on ideas for 'generic' order, and one is a xtfrm(z) function that creates an integer vector that sorts the same as z. Then -xtrfm(z) would work.

>
> ...... if only I would have biked home earlier, today,...
> I'm sure I would have save much of my time....
>
> Martin
>
>>>>>> "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
>
> ______________________________________________
> R-devel_at_r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

-- 
Brian D. Ripley,                  ripley_at_stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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