Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!apple!portal!cup.portal.com!Edward_M_Cherlin
From: Edward_M_Cherlin@cup.portal.com
Newsgroups: comp.lang.apl
Subject: Re: Some General Questions about J
Message-ID: <39727@cup.portal.com>
Date: 2 Mar 91 17:34:48 GMT
References: <1991Feb23.234505.5960@csi.uottawa.ca>
Organization: The Portal System (TM)
Lines: 14

cbbrowne asked for help in understanding J and its rationale. He can find some
of the answers in the article "The Principles of J" in APL News, 22,3 (1990).
The article explains most J features with examples for the more confusing
new features, and shows the development from Sharp (or Reuter:file) APL to
J, starting from before nested arrays and including Dictionary APL. Back
issues are available from the publisher, Springer-Verlag New York, at 800-
SPRINGER or 212/460-1500.

To answer one particular question: instead of using the axis operator to
do reductions in a particular direction, J uses the rank operator. By default,
reduction in J applies along the first axis rather than the last. The rank
operator partitions an array by selecting a specified number of dimensions
from the end. So +/"n applied to an m-dimensional array reduces the (m-n)th
dimension, counting in origin 0.