Indeed a good point Julian that is also a handy idiom for “pairwise” in J.
Note the q version also allows the null (0N) to be placed anywhere in the shape
vector, so if you knew the list had 3 groups, but weren’t sure how many items
in the group then you could also do this:
q)3 0N#args /Comment: From my list of 6 items I know there
are 3 keys … let # determine the groups
"Code" 33
"Name" "Iverson"
"Age” 34
Then in J, the usual
(3,($args)%3)$args NB. Produces the same result as below, but one
only needs to know the “3” rows
The key advantage is simply a “handy benefit”. I recall having to calculate
the shape for these types examples frequently in APL.
@Joseph: Not sure about how this idiom is factored in to the q implementation,
the q version does handle higher rank lists too, but would need to experiment
to determine impact on your idiom.
Rob
> On 22 Aug 2020, at 2:18 am, Julian Fondren <[email protected]> wrote:
>
> On 2020-08-21 10:55, 'Rob Hodgkinson' via Programming wrote:
> ...
>> q)0N 2#args
>> /Comment: q uses the NULL value (0N) to say “I know the
>> list is in pairs, so work out the rows" (hence here 3 x 2)
>> "Code" 33
>> "Name" "Iverson"
>> "Age” 34
>> The equivalent mechanism in APL or J is along these lines:
>> args=: 'Code';33;'Name';'Iverson';'Age';34
>
> _2]\args
> ┌────┬───────┐
> │Code│33 │
> ├────┼───────┤
> │Name│Iverson│
> ├────┼───────┤
> │Age │34 │
> └────┴───────┘
> ----------------------------------------------------------------------
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