how to make the following boxed data from a list

Question

In J, I have a list like 1 2 3, I want to take *: and 2* to make it a box structure like

┌─┬─┐
│1│2│
│4│4│
│9│6│
└─┴─┘

or even

┌───┐
│1 2│
├───┤
│4 4│
├───┤
│9 6│
└───┘

How to do this? I would really appreciate your help.

Answer 1

You need to evoke a gerund in append mode (:0).

a =: 1 2 3
*:`+: (`:0) a
1 4 9
2 4 6

If you need them boxed, just ;/ them:

;/*:`+: (`:0) a
┌─────┬─────┐
│1 4 9│2 4 6│
└─────┴─────┘
;/ |:  *:`+: (`:0) a      NB. different axis
┌───┬───┬───┐
│1 2│4 4│9 6│
└───┴───┴───┘
 _3 <\6 1 $,*:`+: (`:0) a   NB. yet another axis
┌─┬─┐
│1│2│
│4│4│
│9│6│
└─┴─┘

Answer 2

If you want vertical (column-oriented) output, you should first convert your list to vertical (column-oriented) format:

    ,.1 2 3
 1
 2
 3

Now you can apply as many calculations as you like. If you want to put each output in a separate box, you can chain them together using ; in a fork:

    (*: ; 2&*) ,. 1 2 3

Two notes:

• It is unusual, and unnecessary, in J, to use boxes when all your data is the same type and shape. In your case, both your operations are scalar and numeric, and so both verbs will produce a 1x3 column of numbers. It would be more typical and idiomatic to combine them with ,. to produce a 2x3 table of numbers than ; to produce 2 opaque boxes.

• "Double" is already a primitive in J, so instead of 2&*, we could say +: as in (*: ; +:) ,. 1 2 3