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From: cs450a03@uc780.umd.edu
Newsgroups: comp.lang.apl
Subject: RE: Do While in J?
Message-ID: <23MAR91.00430776@uc780.umd.edu>
Date: 23 Mar 91 00:43:07 GMT
References: <MJAB.91Mar22144533@nanna.think.com>
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Well, since I've got J 3.0 with 2.9 docs, I suppose I can answer this
one...  (Note, this has been tested on sun4 J 2.9)

   nz =. ''::'x. }:^:(0=y.) y.'
   3 nz 4
4
   3 nz 2
2
   3 nz 0
3

   f =. 0: . , . nz . ({~) : 1
   data=. 1 0 0 _1 0 0 1 0 0 2 0 0 3
   data f 13 0
0 1 1 1 _1 _1 _1 1 1 1 2 2 2 3
   data f  (#data);i.0
1 1 1 _1 _1 _1 1 1 1 2 2 2 3

   f =. 2&= . , . nz . ({~) : 1
   data f (#data);i.0
1 1 1 _1 _1 _1 1 1 1

(I think, I didn't actually test this last variant, but it matches my
experience)

' given ':{       ger=.  w . g . m . s
                    f  =.  ger : 1
' then: ':{       x f n;<b
' step 0':{       r=.     c=.     b }:i=. _1
' step n':{       r=. r g c=. c m x s i=. i+1

----------------------------------------------------------------------

also,

2 3 5   + . - . * . % :0  4

+-----+-------+-------+-------------+
|6 7 8|_2 _1 1|8 12 20|0.5 0.75 1.25|
+-----+-------+-------+-------------+

(This one's from memory)  
In other words,  you just box the results and stick them together.
Rank is supposed to be maxima of ranks of the argument functions (and
it doesn't have to be 4 functions for :0)

Raul Rockwell

P.S. (3.0 question) does anyone know what transitive n. (moments) is
supposed to do?