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So in my current HubNet application turtles are organized in various graph-structures. Whether or not two clients can see each other depends on whether the corresponding turtles are connected in the graph.

I currently build the graphs based on the turtles who-numbers and have thus built in the assumption that if there are n turtles at any given point these are numbered from 0 to n-1. I expect that this might cause problems if, for instance, a client connects, then drops and then re-connects since this (if I'm not mistaken) will give that client a new who-number (and the old number is not reused). So I'm wondering if there is a way to make sure that the turtles are numbered in the way I want?

Dropping everyone and then resetting who-numbers would be one (bad) solution. Can you help me either by suggesting a better solution or how to implement the bad solution?

Seth Tisue
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ProfessorHelloKittyNr1
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If you want to use who numbers, you'll need to hide the turtles instead of killing them. If that makes things awkward because you find yourself needing to refer to e.g. turtles with [not hidden?], then consider making two breeds, call them actives and inactives or something like that, and then when hiding a turtle do hide-turtle set breed inactives. Then you can always refer to the set of active turtles just as actives. When someone joins the simulation, give them an inactive turtle if there is one, and have it do show-turtle set breed actives.

Or, if you decide not to use who numbers, you'll need a new turtle variable, say you call it id. When you make a new turtle, do set id count turtles - 1. When a turtle dies, you'll need to reassign new id numbers so there aren't gaps anymore. Does it matter exactly what scheme you use for that? Do you need there to be any particular relationship between a turtle's old number and its new number? I can think of several possible different approaches to this. Here's one that assigns the id numbers in ascending order by who number:

let whos sort [who] of turtles
ask turtles [ set id position who whos ]

P.S. But I have to wonder, is all this numbering really necessary? In a normal NetLogo model, it's almost never necessary to use who numbers for anything. There's almost always a simpler way. Why do you feel you need to use numbering in this model? Perhaps you do need it, but I'm at least a little skeptical.

Seth Tisue
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  • Thanks! Perfect. So the reason I use the who-numbers is that I felt that when randomly allocating turtles to places in various graphs it was useful to have some enumeration of the turtles. For instance, if I want to create a circle I do this by combining turtle n with turtle n-1 and n+1 (and make special adjustments for the last turtle). Is there an easier way to do this? – ProfessorHelloKittyNr1 Feb 12 '14 at 22:09
  • Making links between turtles in a circle is a case where going by the who numbers is probably actually the simplest solution. – Seth Tisue Feb 13 '14 at 00:04
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    Now that the NW extension is bundled with NetLogo, [`nw:generate-ring`](http://ccl.northwestern.edu/netlogo/docs/nw.html#generate-ring) is a convenient way to create a circle of turtles connected by links. – Nicolas Payette Mar 09 '15 at 23:30