Selecting an item from a list in Netlogo - netlogo

Question

I'd need to pick an object in a bag containing 20 elements with attributes c (color) and s (size). Both color and size are numbers (e.g. c= {red = 256, black = 0, ... } = {256, 0, ...}).
As in Python I'd use random.choice in numpy library, I found on the web that the corresponding function in Netlogo is the extension rnd.
Struggling along a possible solution, I did
Edited:
breed[people person]
people-own
[
ball
size
color
bag
]
to setup
create-people 5
[ set color gray
setxy random-xcor random-ycor
]
ask people[
set bag [ ] ; 0 items
]
end
To create the balls:
to create-balls
set color random 300 ; color
set size random-float 5 ; size
let this-ball self
ask one-of people [ ; ask one of people to put the ball created into the bag
set bag fput this-ball bag ; add ball to the bag
]
end
The code below should include the part of drawing:
to draw
ask one-of people [
rnd:weighted-one-of bag [ ] ; I do not know what I'd write in the brackets
]
end
As you can easily see, I've many doubts about how to implement the code.
How can I select one item from the bag depending on its size (or color)?
Can you please help me out with it?

Answer 1

Here is a complete model that creates people and balls as turtle agents and has 30 of the balls get chosen weighted by their size. It then opens an inspect window for the person who has chosen the most balls.
extensions [rnd]
breed [people person]
people-own [ my-balls ]
breed [balls ball]
balls-own [ chosen? ]
to setup
clear-all
create-people 20
[ setxy random-xcor random-ycor
set my-balls (turtle-set nobody)
]
create-balls 50
[ hide-turtle
set size one-of [1 2 3 4 5]
set color one-of [red white blue yellow]
set chosen? false
]
repeat 30 [draw-ball]
inspect max-one-of people [count my-balls]
end
to draw-ball
ask one-of people
[ let bag-of-balls balls with [not chosen?]
let choice rnd:weighted-one-of bag-of-balls [size]
ask choice [set chosen? true]
set my-balls (turtle-set my-balls choice)
]
end
Some things to notice:
There are NO lists in this code. There are situations where you should use lists. Common uses include memory where the order is important (eg you only want to keep track of the last 5 other people seen) or where the same agent can appear multiple times. And the list commands are very powerful. However, unless you need a list then you should use agentsets.
Each person has their own bag called 'my-balls' that contains the balls they select. That is initialised as a turtle-list as part of the setup.
I used a variable called 'chosen?' that is owned by each ball to track whether it is still in the bag for the next person to choose. Then the bag-of-balls is created only as all the balls not yet chosen.
The code for weighted random choice (when choosing from agentsets) simply has the name of the variable holding the weight as the reporter, but you could use some function such as rnd:weighted-one-of bag-of-balls [size ^ 2] if you wanted a more complicated weighting scheme.