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From: rjfrey@kepler.com (Robert J Frey)
Newsgroups: comp.lang.apl
Subject: Re: WANTED:  a way to sort array so each column i
Message-ID: <565@kepler1.kepler.com>
Date: 18 Apr 91 00:30:54 GMT
References: <31931@usc> <13APR91.22583472@uc780.umd.edu> <WEG.91Apr14120440@convx1.convx1.ccit.arizona.edu>
Reply-To: rjfrey@kepler1.UUCP (Robert J Frey)
Organization: Kepler Financial Management, Ltd., Setauket, NY.
Lines: 36

In article <WEG.91Apr14120440@convx1.convx1.ccit.arizona.edu> weg@convx1.ccit.arizona.edu (Eythan Weg) writes:
>In article <13APR91.22583472@uc780.umd.edu> cs450a03@uc780.umd.edu
>(Raul Rockwell) writes:
>
>
>   A Analla writes:
>
>   >Could some please suggest a generic function to reorder each column
>   >of an array in descending order where the array is two dimensional.
>
>Incidentally, how does one write this function in APL2?
>
>Eythan Weg

In Dyalog APL, which is similar to APL2, one could do:

	A[; gradedown rotate A]

This would generalize to simple arrays, character or numeric, of any dimension.

If this use of grade(down/up) generalizes like this in APL2, then I might try:
	
	A[; gradedown[1] A]


because (from what I remember) APL2 is rather general in its use of the axis
"operator". I don't know if this last bit works, however.

In vanilla APL there are some cases that can be handled pretty simply. For
example, if A is a 5 by 10 numeric matrix whose elements are all positive
numbers less than or equal to 100, then this does the job:

	A[; gradedown(5 reshape 100)decode A]

This last "solution" has some serious overflow and truncation problems if A
results in decoded values which are too large.