# [PD] array-abs

Jonathan Wilkes jancsika at yahoo.com
Mon Oct 5 09:16:13 CEST 2015

```Yes that's true about iterative approaches and dataflow in general.
What gets me about [list-drip] is the necessity of the [>> 1] to prevent
stack overflow.  So even if you can follow the order of operations with
recursion through that object chain, you have to also keep track of
the order in which those two branches interact during the recursion.

I can visualize that using a small set of data to the inlet, and taking my time.
But at that point the diagram itself isn't elucidating anything useful about
the flow of data.  For that you'd need some way to animate the flow through
the wires in greater than zero logical time.  And even then you'd want to show
the actual data associated with each cycle of animation.

-Jonathan

On Monday, October 5, 2015 1:59 AM, Matt Barber <brbrofsvl at gmail.com> wrote:

Not supporting recursion in a dataflow environment is not a huge problem IMO, especially since so many classically recursive problems (binary search, quick sort, etc.) can be solved iteratively. The iterative solution is almost always going to be clearer in an environment like Pd.
[list-drip] is a decent model for how recursion would have to work -- [list-rdrip] even more, since it can take advantage of the native right-to-left output to reduce the number of objects. Anything solved using a divide-and-conquer strategy could even be a bit faster using the stack vs. an until loop. A while back I made a kind of clunky iterative quick sort; I wonder if it would be possible to throw ranges to partition onto Pd's stack without it overflowing ... probably not since there's nothing to guarantee that quick sort doesn't run at O(n^2) in the worst case. Binary search almost certainly could; I'll do that in the next few days and post benchmarks comparing an [until] loop solution with recursion.
On Sun, Oct 4, 2015 at 4:12 PM, Jonathan Wilkes <jancsika at yahoo.com> wrote:

I think matju wrote the [list-drip] algorithm partly to show the difficultyof using recursion in Pd.  That the actual author of Pd's messagingsystem refrains from using recursion to solve the same problem addsweight to that point.
-Jonathan

On Sunday, October 4, 2015 3:45 PM, Matt Barber <brbrofsvl at gmail.com> wrote:

It takes almost a full second to output a list of n=1,000,000 with a 100-cycle until on my computer.
On Sun, Oct 4, 2015 at 3:38 PM, Matt Barber <brbrofsvl at gmail.com> wrote:

This is still much slower than [list-drip], and it freezes Pd for me when I get up to lists of n=100,000 or so. I think it's because Pd has to copy the list to an output every cycle of [until], so when n=10, you're only outputting something of size 10 10 times, but that grows by n^2 so when it's n=10,000 times 10,000 outputs, it's a lot. 1,000,000 seems impossible unless the list decreases in size each cycle, which it does in [list-drip], recursively.
On Sun, Oct 4, 2015 at 2:48 PM, Miller Puckette <msp at ucsd.edu> wrote:

Here's a way to serialize a list in (I believe) linear time:

#N canvas 881 291 450 300 10;
#X msg 136 14 list 3 . 1 4 1 5 9;
#X obj 83 97 list length;
#X obj 77 211 list split;
#X obj 101 186 list;
#X obj 139 55 t l b l;
#X obj 83 119 until;
#X obj 83 141 f;
#X obj 114 142 + 1;
#X msg 166 117 0;
#X obj 83 163 t b f;
#X obj 117 278 print;
#X obj 116 250 list split 1;
#X connect 0 0 4 0;
#X connect 1 0 5 0;
#X connect 2 1 11 0;
#X connect 3 0 2 0;
#X connect 4 0 1 0;
#X connect 4 1 8 0;
#X connect 4 2 3 1;
#X connect 5 0 6 0;
#X connect 6 0 7 0;
#X connect 6 0 9 0;
#X connect 7 0 6 1;
#X connect 8 0 6 1;
#X connect 9 0 3 0;
#X connect 9 1 2 1;
#X connect 11 0 10 0;

cheers
Miller

On Sun, Oct 04, 2015 at 02:27:37PM -0400, Matt Barber wrote:
> Your [pd drip] does a lot of extra work. It's go basically linear stack
> performance, and you're recopying the list every loop (an until loop would
> solve this for a little extra cpu time). The secret of [list-drip] is that
> it doesn't recopy the list using the [list] object, and it avoids stack
> overflows by doing the recursion split at the midpoint of the list and only
> outputting when it's done the binary split down to lists of size 1, which
> are the elements, or size zero, which are bangs (and which are filtered
> out).
>
> Since it's binary recursion on the list, the stack only grows
> proportionally to log_2(n), which is about 20 for n=1,000,000. It's still
> going to be slower than an object written in C that can just iterate over
> the contents in a single loop, and lists in Pd are slower in general than
> arrays, so an until loop and tabread over an array is going to be quicker.
> It is much slower for copying though -- an until loop with tabread and
> tabwrite has way more overhead than an [array get]-[array set] pair.
>
>
> On Sun, Oct 4, 2015 at 1:06 PM, Christof Ressi <christof.ressi at gmx.at>
> wrote:
>
> > Please don't use the previous version of the multi-dimensional arrays!!!
> > First, I forget to get rid of one [drip] object. Second, I discovered that
> > [pd drip] will create a stack overflow if there are more than ca. 300
> > elements! (Why???) So I replaced it with [list-drip] which works fine.
> >
> > So here's the corrected pure vanilla version + a zexy version using
> > [drip]. I prefer to use the latter one because it's waaaaay faster than all
> > the drip abstractions based on [list split].
> >
> > Vanilla: https://www.dropbox.com/s/wd0avxtaneqgdic/carray_vanilla.zip?dl=0
> > Zexy: https://www.dropbox.com/s/ea8kihwbdqhcajr/carray_zexy.zip?dl=0
> >
> > Christof
> >
> > PS:  I did a benchmark test of iterating through an array of 1 million
> > elements, using [realtime], and here's what I found on my system:
> >
> > [array get] + [drip] --> ca. 6.5-9ms
> > [until] + [tabread] --> ca. 120-200ms
> > [array get] + [list-drip] --> ca. 340-400ms
> >
> > To me this result was a bit surprising...
> >
> > You can test yourself with the attached patch.
> > *Gesendet:* Sonntag, 04. Oktober 2015 um 17:32 Uhr
> > *Von:* "Christof Ressi" <christof.ressi at gmx.at>
> > *An:* "Matt Barber" <brbrofsvl at gmail.com>
> >
> > *Cc:* Pd-List <pd-list at lists.iem.at>
> > *Betreff:* Re: [PD] array-abs
> > Wow, looks cool!
> >
> > Just a few days ago I reworked some of my personal table abstractions,
> > which also make use of the [array] object. However, some of them depend on
> > zexy externals (I hope I didn't miss any other dependencies). I haven't
> > shared them yet so the documentation is quite poor (no help files, docs
> > inside the abstraction) and they look a bit messy. But maybe you can get
> > some inspiration for your library...
> > https://www.dropbox.com/s/xvj031korqw8guf/ctab-abs.zip?dl=0
> >
> > Additionally I've been working on three basic abstractions for creating,
> > setting and reading multi-dimensional arrays of any number of dimensions.
> > They are pure vanilla style and even come with a help file :-D.  (a object
> > for array resizing is yet to be done...)
> > https://www.dropbox.com/s/6xfgdyt697138e6/carray.zip?dl=0
> >
> > Would be cool to hear your opinion on the multi-dimensional array stuff!
> >
> > Christof
> >
> >
> >
> >
> > *Gesendet:* Samstag, 03. Oktober 2015 um 22:32 Uhr
> > *Von:* "Matt Barber" <brbrofsvl at gmail.com>
> > *An:* "IOhannes m zmölnig" <zmoelnig at iem.at>
> > *Cc:* Pd-List <pd-list at lists.iem.at>
> > *Betreff:* Re: [PD] array-abs
> > Thanks.
> >
> > Yes. Right now I'm just looking to see if these would be useful, if
> > there's anything awful about the syntax, if they try to do too much or are
> > too fussy, if anyone would want to contribute, etc. When I get them
> > polished a bit I'll do a regular release on the normal channels (I can't
> > remember if I have access to anything officially Pd related).
> >
> > Matt
> >
> > On Sat, Oct 3, 2015 at 4:22 PM, IOhannes m zmölnig <zmoelnig at iem.at>
> > wrote:
> >>
> >> hi,
> >>
> >> great!
> >>
> >> On 10/03/2015 07:36 PM, Matt Barber wrote:
> >> >
> >> > https://www.dropbox.com/s/45tk62dpz0z2mqo/array-abs.zip?dl=0
> >> >
> >>
> >> db?
> >>
> >> would you like to put those on a version control system of sorts, e.g.
> >> the puredata svn or some publicly available git repository (e.g. github)?
> >>
> >> (read as: please let us not go back to the dark ages, where code was
> >> shared by sending files around by on floppy disks and you never new
> >> which version was the current one)
> >>
> >> fgmards
> >> IOhannes
> >>
> >>
> >>
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