Difference in defining a variable - netlogo

Question

I would like to define a new object, and I do not know what could be the best approach.
I know that let is used for local variables and this should be the main difference.
I am creating a list in NetLogo that stores elements with some attributes/properties. Since later I will need to pick one of this item up from the list created, what I would need to understand if I need to create the object as a local variable or a global(turtle’s own) variable to do this.
The two possible cases should be:
1) Create object as a global variable:
globals [object
attribute]
turtles-own[
my-list]
to setup
create-turtles 5
ask turtles [
set my-list []
]
end
to-go
ask one-of turtles[
set attribute 5
set my-list lput object my-list]
end
2) Create object as a local variable:
turtles-own[
my-list]
to setup
create-turtles 5
ask turtles [
set my-list []
]
end
to-go
ask one-of turtles[
let object “New object”
let attribute 5 ; this should be assigned to object
set my-list lput object my-list]
end`
There should be also another case, i.e. object and attribute defined in turtles-own (this is the case that I would prefer):
turtles-own[
object
attribute
my-list]
to setup
create-turtles 5
ask turtles [
set my-list []
]
end
to-go
ask one-of turtles[
set object “New object”
set attribute 5 ; this should be assigned to object
set my-list lput object my-list]
end
What I would need to implement is the following:
Turtles who have objects stored in a list
Objects who have attributes (or also you can interpret it as turtles that create objects with attributes)
Turtles that can choose to pick an object up from that list depending on the attribute. (This is the most important point as I need to work with the object and its attributes later).
Could you please help me to understand how I need to implement it?
I would like to avoid hatch or create a breed for object because I am not sure to be able to manage it throughout the code.
However, if this is the only right way to proceed, I will do it.
Thank you for your time.

Answer 1

Val, I realize you initially asked "I would like to ask you the difference in using let and set." but later you explain what you need implemented, which is what I answered. So, the title of this question is not very accurate.
I'm not sure this is the only way to proceed but I tried to solve your problem, as I understand it, using two breeds ( people and objects ). I hope you can see from the code below how to do that -- just don't use "ask-turtles" anywhere unless you want to affect both people and objects.
Of course post questions here if you run into problems.
Working code is below.
The way I interpreted your question,
objects are persistent and global,
changes to an object's attributes by anyone at any time will update
the value of that attribute for that object in every agent's my-list
each person has their own my-list of objects, possibly empty.
the my-lists of different agents will be different
each person might search for one of the objects from their list, based on the attribute, and I stored the resulting object, if any, in their current-choice.
each person should be able to select any of the objects and add that object
to their my-list
Implementation design choices:
Use two breeds, "people" and "objects" which own different variables.
Each object owns an attribute and an object-type ( such as "apple" or "orange")
Each person owns a my-list and current-choice. my-list is a list, and
current-choice is an agent ( possibly = nobody )
Features of the code below
The code creates 5 people and 6 objects for testing purposes. All of them are just left sitting at the origin on the display.
At each iteration of the "go" step, a random person selects two random objects and adds them to their my-list, and then locates one of them based on an attribute value.
the code makes a list of all objects in my-list that have the desired attribute,
which may have zero, one, or more objects in it, and does something sensible based on
the length of the list.
no items are ever removed from my-list, or checked to see if they are already there.
that's all this does. run setup, run go (once), and inspect the results.
I hope this is helpful. Let me know here if I didn't answer your question.
Wade
;; this is the second version of the code. It has some comments removed or
;; corrected, and initializes current-choice to nobody instead of []
globals [found?] ;; keep track of whether we found an object
breed [objects object]
breed [people person]
objects-own [
object-type ; say "apple" or "orange" or "widget"
attribute ; user defined, apparently an integer
]
people-own[
current-choice ; an agent
my-list] ; a list of objects
to setup
clear-all
make-people
make-objects
reset-ticks
end
to go
;; for debugging we'll push two objects onto the my-list for a random agent
;; then find one of them with the right attributes and pull it into current-choice
ask one-of people[
;; select a random apple, set its attribute to 111,
;; and push it onto this turtle's my-list
set current-choice one-of objects with [object-type = "apple"]
ask current-choice [set attribute 111 ]
set my-list ( lput current-choice my-list )
;; select a random orange, set its attribute to 222,
;; and push it onto this turtle's mylist
set current-choice one-of objects with [object-type = "orange"]
ask current-choice [set attribute 222 ]
set my-list ( lput current-choice my-list )
;; ok, let's see if we can find an object in my-list with attribute 111
let want-attribute 111 ;; for debugging purposes
;; make a list of ALL objects on the list with the desired attribute
;; as far as we know,there may be many, one, or zero objects with this attribute
let found-list filter [ i -> want-attribute =[attribute] of i ] my-list
if-else length found-list > 0
[ ;; we found at least one match
set found? true
;; pick a random object from the list of objects which have the desired attribute
set current-choice one-of found-list
]
[ ;; we didn't find any matches
set current-choice nobody
set found? false
;; do whatever you do when there is no matching object
]
;; if desired, check out how things ended up by uncommenting the next
;; two lines:
;; inspect current-choice
;; inspect self
]
tick ;; update the tick counter
end
to make-people
create-people 5
[
set current-choice nobody
set my-list []
]
end
to make-objects
create-objects 3 ; create 3 apples
[ set object-type "apple"
set attribute 333 ]
create-objects 3 ; create 3 oranges
[ set object-type "orange"
set attribute 555 ]
end
;; Above code was created by Wade Schuette, 3-November-2019
;; modified sightly 4-November-2019
;; No copyright is claimed. Enjoy!