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From: jaxon@sp27.csrd.uiuc.edu (Greg P. Jaxon)
Newsgroups: comp.lang.apl
Subject: Re: Grade Down Columns of An Array
Message-ID: <1991Jun25.202455.15259@csrd.uiuc.edu>
Date: 25 Jun 91 20:24:55 GMT
References: <33789@usc.edu>
Sender: news@csrd.uiuc.edu (news)
Organization: UIUC Center for Supercomputing Research and Development
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It seems we just went through this topic a month ago, it must be an
assigned puzzle.  Here is a standard APL solution, but there are far more
efficient APL2-style solutions.

 $   Z is COLUMN_SORT A;#IO;#CT;T
[1]  #IO is #CT is 0
[2]  T is reverse rho A
[3]  Z is grdn  A is ,A
[4]  Z is A[transpose T rho Z[grup T[0]|Z]]
 $
 
Greg Jaxon

P.S. I wouldn't turn this in to an APL instructor unless
I could identify which primitive function is using #CT!