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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> >
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