Pxrand repeating elements in a row

Questions
#1

I’m running into something very strange in the context of a larger script that means that I either misunderstand what Pxrand does, or there’s a bug or something …?

I’m testing the most basic Pxrand script and outputting to the post window:

var g = Pxrand.new([1,2,3,4,5,6,7,8,9,10], inf);
g.asStream.next

When I run this I can see that numbers from the list are repeated multiple times in a row, quite frequently. My understanding is that Pxrand is meant to avoid this exact behaviour so that that same item is never repeated consecutively.

Here’s what I’m seeing in the console:

-> a Pxrand
-> 9
-> 4
-> 1
-> 2
-> 4
-> 9
-> 3
-> 1
-> 5
-> 9
-> 5
-> 10
-> 2
-> 3
-> 9
-> 9
-> 5
-> 3
-> 3
-> 4
-> 8
-> 5

You can see that there’s a double 9 and a double 3 in there, sometimes it repeats even more often.

Am I misunderstanding something? Or is something else going on?

Thanks for any help!

#2

Welcome to the forum @emenel!

There is no bug here. You can think of a pattern as a blueprint for a machine, and a stream as the actual constructed machine. Every time you run g.asStream, you are creating a new stream from that blueprint, independent of any other stream created from the same pattern object. For example, consider the same code using Pseq instead of Pxrand:

g = Pseq.new([0, 1, 2], inf)
g.asStream.next

If you evaluate this multiple times, you’ll only ever see 0, because you are just asking for the first value of a new stream each time.

What you want instead is:

h = g.asStream;
h.next; // this you can evaluate repeatedly to get the results you want

you can also use g.asStream.nextN(n) to get the first n values from the stream.

Hope this helps.

1 Like
#3

Thank you! Yes, this clears it up and helps me better understand how streams work.

1 Like
#4

Hi and welcome !

you are not posting the whole code but I assume generating new Streams from a Pxrand Pattern in each loop is causing the repetitions. This is touching the crucial difference between Patterns and Streams (see James Harkins’ Pattern Guide for this and other Pattern subtleties)

// failing
(
g = Pxrand.new([1,2,3,4,5,6,7,8,9,10], inf);
100.do { g.asStream.next.postln };
)

(
100.do { 
	g = Pxrand.new([1,2,3,4,5,6,7,8,9,10], inf);
	g.asStream.next.postln 
};
)

// correct
(
g = Pxrand.new([1,2,3,4,5,6,7,8,9,10], inf).asStream;
100.do { g.next.postln };
)
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#5

Yep, that’s precisely the issue I was running into… I don’t think I fully grokked the relationship between the Pattern and the Stream, and was thinking of the stream as a direct reference to the pattern, but just returning values in a different way. I didn’t full get that each stream is independent and only references the the pattern as a source.

I think I understand it better now! Thanks for your quick help.

1 Like