How to force turtles to move only in a half of the world? - netlogo

Question

I created a world divided in two parts with the command ask patches with [ pxcor < 0] [set pcolor blue] ask patches with [pxcor > 0] [set pcolor green] .
In one of this there're 100 turtles, who 5 are infected and the same in the other part.
My problem is to force the turtles to move only in their part of the world. So I want that turtles with pcolor = blue move randomly in the second and third quadrant (pxcor <0) and turtles with pcolor = green in the first and fourth quadrant (pxcor> 0). how do I do?
This is the code:
turtles-own
[
sick?
sick-time]
to setup
ca
ask patches with [ pxcor < 0 ] [set pcolor blue] ; we want divide the world in two parts: the blue one in the north of Italy
ask patches with [pxcor > 0 ] [set pcolor green]; the white one is the south of Italy
ask patches with [pxcor = 0 ] [set pcolor white ] ; represent the border
create-turtles 200 ; we create a population made up for 200 people
[ set size 1
set shape "person"
set sick-time 0
get-healthy]
ask n-of 100 turtles ; 100 of this one live in north of Italy
[setxy 12 random-ycor ]
ask n-of 100 turtles ; another 100 in the south
[setxy -12 random-ycor
]
ask n-of 5 turtles with [pcolor = blue] ; we want infect 5 people for each world
[get-sick ]
ask n-of 5 turtles with [pcolor = green]
[get-sick ]
reset-ticks
end
to get-healthy
set sick? false
set color white
end
to get-sick
set sick? true
set color yellow
set shape "circle"
set sick-time sick-time + 1
end
to go
ask turtles
[
move ]
tick
end
to move
rt random-float 360
fd 1
end

Answer 1

Your movement procedure looks like:
to move
right random-float 360
forward 1
end
If you want them to just stay where they are if moving would take them into the wrong half, then you can use patch-ahead to test the patch they'd be moving to. I think what you want is that they don't go to a different coloured patch. One way is:
to move
right random-float 360
if [pcolor] of patch-ahead 1 = pcolor [forward 1]
end
[pcolor] of patch-ahead 1 returns the colour of the patch that is one distance unit ahead, so where the turtle is trying to move to. pcolor is the colour of the patch that the turtle is currently standing on.