[Rd] rank(*) with NAs -- new option "keep" desired

[Gabor Grothendieck]

I could have used this also.  Currently I do this:

z <- ifelse(is.na(y),NA,rank(y))
names(z) <- names(y)

The following also works but is less transparent:

z <- y
z[z==z] <- rank(y)

Another extension of rank that could be useful would be to have
an argument that causes it NOT to do tie averaging.  This is useful
when you are using rank(x) in the sense of an inverse permutation.
Currently I do this:

z <- order(order(y))
names(z) <- names(y)


--- Martin Maechler <maechler at stat.math.ethz.ch> wrote:
>In some contexts, I find the current behavior of rank() very
>`suboptimal'.
>
>We have the argument na.last = {TRUE | FALSE | NA }
>where the first two cases treating NAs (almost) as if they were
> == +Inf or == -Inf  whereas the 3rd case just drops NAs.
>For the typical ``Rank Transformation'' that is recommended in
>EDA in several contexts, I would however want something else,
>namely keep the NAs !
>
>An example -- including the new option as I'm proposing it ---
>makes things more clear :
>
>> y <- c(2:1,NA,0)
>> rank(y, na.last = TRUE)## ==== rank(y)
>[1] 3 2 4 1
>> rank(y, na.last = FALSE)
>[1] 4 3 1 2
>> rank(y, na.last = NA)
>[1] 3 2 1
>> rank(y, na.last = "keep") ### <<<<< NEW >>
>[1]  3  2 NA  1
>> 
>---
>
>Alternatively to extending the possible values of `na.last' I
>first thought of a new (boolean) argument, but found the current
>solution less ugly.
>
>Feedback welcome!
>
>Martin Maechler <maechler at stat.math.ethz.ch>	http://stat.ethz.ch/~maechler/
>Seminar fuer Statistik, ETH-Zentrum  LEO C16	Leonhardstr. 27
>ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
>phone: x-41-1-632-3408		fax: ...-1228			<><
>
>PS: Stumbled over this while implementing  cor.test()s
>    method = c("pearson", "spearman", "kendall")  for  cor()
>    itself.
>
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