Ethejiesa, I stand corrected! Your solution works.
Thanks!
On Mon, May 24, 2021 at 2:40 PM Raoul Schorer <raoul.scho...@gmail.com>
wrote:
> Hi and thanks to all for helpting!
>
> Raul, I think you forgot to copy your working verb in your last.
> Ethejiesa, good catch and great insight! Your verb yields a domain error
> on J902, though.
>
> Cheers,
> Raoul
>
> On Mon, May 24, 2021 at 2:35 PM Raul Miller <rauldmil...@gmail.com> wrote:
>
>> Thank you, that makes sense.
>>
>> And, I also see that I built a faulty value for ast.
>>
>> Here's a fixed ast and a working depth vector verb:
>>
>> t=:'.'
>>
>> ast=:t;(t;t);(t;(t;t);t);<(t;(t;t;t);(t;t;t);t)
>>
>> ast
>>
>> +-+-----+-----------+---------------------+
>>
>> |.|+-+-+|+-+-----+-+|+-+-------+-------+-+|
>>
>> | ||.|.|||.|+-+-+|.|||.|+-+-+-+|+-+-+-+|.||
>>
>> | |+-+-+|| ||.|.|| ||| ||.|.|.|||.|.|.|| ||
>>
>> | | || |+-+-+| ||| |+-+-+-+|+-+-+-+| ||
>>
>> | | |+-+-----+-+|+-+-------+-------+-+|
>>
>> +-+-----+-----------+---------------------+
>>
>> dv ast
>>
>> 0 1 2 1 2 3 2 1 2 3 3 2 3 3 2
>>
>>
>> (Apologies for any wonky formatting -- I am on a phone right now.)
>>
>>
>> Thanks,
>>
>>
>> --
>>
>> Raul
>>
>> On Mon, May 24, 2021 at 2:47 AM ethiejiesa via Programming <
>> programm...@jsoftware.com> wrote:
>>
>> > Raoul Schorer <raoul.scho...@gmail.com> wrote:
>> > > Dear all,
>> > >
>> > > I am struggling with the translation of the following APL dyad to J:
>> > >
>> > > ∊ 0 {(⊢,(⍺+1)∇⊣)/⌽⍺,1↓⍵} y
>> > >
>> > > which is the expression to yield a depth vector from a tree in record
>> > > format (drawn from Dr. Hsu's thesis). Demo:
>> >
>> > Oh cool! I have been (very sparingly) messing about with Hsu's tree
>> > representation. For purely selfish reasons, I haven't looked at the
>> thesis,
>> > trying to figure out the representation myself. However, I have only got
>> > so far
>> > as figuring out an algorithm for non-recursively generating random depth
>> > vectors.
>> >
>> > > t ← '∘'
>> > > ast ← t (t t) (t (t t) t) (t (t t t) (t t t) t)
>> > > ∊ 0 {(⊢,(⍺+1)∇⊣)/⌽⍺,1↓⍵} ast
>> > > 0 1 2 1 2 3 2 1 2 3 3 2 3 3 2
>> > >
>> > > In particular, I don't understand the control flow and termination
>> > > condition for the recursion. Dr. Hsu says that this uses tree
>> reduction
>> > > with no base case.
>> >
>> > Anyway, my APL is pretty sketchy, but it looks like the ast
>> representation
>> > there is something like this:
>> >
>> > 1) First element of list is node content,
>> > 2) Following nodes are child subtrees.
>> >
>> > So the algorithm should be conceptually simple. Replace the head atom
>> with
>> > the
>> > current depth, bump current depth, and then recurse over the child
>> > subtrees. I
>> > believe that the "base case" is taken care of by (/), since at the
>> leaves
>> > it
>> > should be operating on atoms.
>> >
>> > > dv =. {{ (];(>:x) dv [)/\ |.x;}.y }}
>> > >
>> > > results in an infinite loop. What am I missing? Is there some kind of
>> > > implicit termination condition in the ∇ primitive?
>> >
>> > The main problem is the (x;}.y) part. The recursion depends on the fact
>> > that
>> > (⍺,1↓⍵) equals ⍺ at the leaves, but (x;}.<'anything') is the same thing
>> as
>> > (x;a:). Thus when y is a leaf, (x;}.y) turns into a tree!
>> >
>> > We can brute for a fix by replacing the (;) in (x;}.y) with
>> > (;`(<@[)@.(0=#@])):
>> >
>> > t=: '.'
>> > ast=: t;(t;t);(t;(t;t);t);<(t;(t;t;t);(t;t;t);t)
>> > f=: {{(],(>:x) f >@[)/ |. x ;`(<@[)@.(0=#@]) }.y}}
>> > 0 ;@f ast
>> > 0 1 2 1 2 3 2 1 2 3 3 2 3 3 2
>> >
>> > Hope that's somewhat comprehensible.
>> > ----------------------------------------------------------------------
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>> >
>> ----------------------------------------------------------------------
>> For information about J forums see http://www.jsoftware.com/forums.htm
>>
>
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