[Jprogramming] Indices of a matrix

[Ben Gorte - CITG]

How about:
 4$.$. i.3 4
0 1
0 2
0 3
1 0
1 1
1 2
1 3
2 0
2 1
2 2
2 3
   4$.$. i.2 3 4
0 0 1
0 0 2
0 0 3
0 1 0
0 1 1
0 1 2
0 1 3
0 2 0
0 2 1
0 2 2
0 2 3
1 0 0
1 0 1
1 0 2
1 0 3
1 1 0
1 1 1
1 1 2
1 1 3
1 2 0
1 2 1
1 2 2
1 2 3

(thanks to Marshall Lochbaum iirc)
Ben
_______________________________________
From: Programming [programming-bounces at forums.jsoftware.com] on behalf of Skip Cave [skip at caveconsulting.com]
Sent: Wednesday, January 11, 2017 00:05
To: Programming at jsoftware.com
Subject: [Jprogramming] Indices of a matrix

Given a 3x4 matrix:



  a =. i. 3 4

  a

0 1  2  3

4 5  6  7

8 9 10 11



I can get the horizontal indices:



   4|a

0 1 2 3

0 1 2 3

0 1 2 3





How do I get the vertical indices?



  3?a   NB. The question-mark represents the unknown verb

0 0 0 0

1 1 1 1

2 2 2 2



Ultimately, I want to design a verb bix, that will take a list of
dimensions of any length, and generate boxed indices of the resulting
array. The number of integers in each box will be the same as the rank of
the array:




  bix 10

┌─┬─┬─┬─┬─┬─┬─┬─┬─┬─┐

│0│1│2│3│4│5│6│7│8│9│

└─┴─┴─┴─┴─┴─┴─┴─┴─┴─┘



  bix 3 4

┌───┬───┬───┬───┐

│0 0│0 1│0 2│0 3│

├───┼───┼───┼───┤

│1 0│1 1│1 2│1 3│

├───┼───┼───┼───┤

│2 0│2 1│2 2│2 3│

└───┴───┴───┴───┘


  bix 2 3 4

┌─────┬─────┬─────┬─────┐

│0 0 0│0 0 1│0 0 2│0 0 3│

├─────┼─────┼─────┼─────┤

│0 1 0│0 1 1│0 1 2│0 1 3│

├─────┼─────┼─────┼─────┤

│0 2 0│0 2 1│0 2 2│0 2 3│

└─────┴─────┴─────┴─────┘

┌─────┬─────┬─────┬─────┐

│1 0 0│1 0 1│1 0 2│1 0 3│

├─────┼─────┼─────┼─────┤

│1 1 0│1 1 1│1 1 2│1 1 3│

├─────┼─────┼─────┼─────┤

│1 2 0│1 2 1│1 2 2│1 2 3│

└─────┴─────┴─────┴─────┘
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