[Jprogramming] Selecting trains with m at .v

[Jimmy Gauvin]

Hi,

The first vocabulary is full of information. So much so that it is easy to
overlook lots of "tasty tidbits".
The answer your question " where is that first explained to the J Beginner
? " , it is not so much explained but rather demonstrated.
I had to change my reading style from "passive assimilation of information"
to "active comprehension of the text and its implications".

Some tidbits are never repeated (due to Roger's preference for conciseness
[this being pure speculation]).

For example, one day I was looking for the equivalent of APL's expand
function:
      1 0 1 0 1 0 0 1\1 2 3 4
  1 0 2 0 3 0 0 4

This is tucked away as a note in :
https://www.jsoftware.com/help/dictionary/d202n.htm

6.  The following cases merit special mention:
   p:^:_1 n gives the number of primes less than n, denoted by π(n) in math
   q:^:_1 is */

   b&#^:_1 where b is a boolean list is Expand (whose fill atom f can be
specified by fit, b&#^:_1!.f or #^:_1!.f )

   a&#.^:_1 produces the base-a representation
   !^:_1 and !&n^:_1 and n&!^:_1 produce the appropriate results
   {= and i."1&1 are inverses of each other; these convert between integer
permutation vectors and boolean permutation matrices

On Sat, Dec 7, 2019 at 1:18 PM 'Jim Russell' via Programming <
programming at jsoftware.com> wrote:

> As shown throughout the Vocabulary.
> But where is that first explained to the J Beginner?
>
> > On Dec 7, 2019, at 1:08 PM, Jimmy Gauvin <jimmy.gauvin at gmail.com> wrote:
> >
> > Hi,
> >
> > note also that the shape of the results can vary considerably :
> >
> > 1 2 3 (+ ; * ; - ; +/ ; ,&4 5) 6 7 8
> > ┌──────┬───────┬────────┬───────┬─────────────────┐
> > │7 9 11│6 14 24│_5 _5 _5│7  8  9│6 7 8 4 5 0 0 0 0│
> > │      │       │        │8  9 10│6 7 8 4 5 4 5 0 0│
> > │      │       │        │9 10 11│6 7 8 4 5 4 5 4 5│
> > └──────┴───────┴────────┴───────┴─────────────────┘
> >
> >
> >
> > On Sat, Dec 7, 2019 at 10:23 AM 'Jim Russell' via Programming <
> > programming at jsoftware.com> wrote:
> >
> >> Lovely! Not at all obvious (to me)until you do it with simple verbs.
> >>
> >>> On Dec 7, 2019, at 9:30 AM, Jimmy Gauvin <jimmy.gauvin at gmail.com>
> wrote:
> >>>
> >>> Hi,
> >>>
> >>> is the following what you want ?
> >>>
> >>>  1 2 3 (+ ; * ; -) 6 7 8
> >>> ┌──────┬───────┬────────┐
> >>> │7 9 11│6 14 24│_5 _5 _5│
> >>> └──────┴───────┴────────┘
> >>>
> >>
> > ----------------------------------------------------------------------
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>
> ----------------------------------------------------------------------
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>