How to choose only one of the item to run from a list?

Question

I am working on a model to simulate the development model. Now, there is a tricky problem returned in my codes:

to develop
grow-population
ask patches with [pcolor = grey][ask neighbors [set potential (potential + one-of [1 -1])]]
ask patches [ set new-potential (potential + sum [potential] of neighbors4) / 5 + one-of [1 -1] ]
ask patches [ set potential new-potential
              set development_patch patches with
                  [potential > threshold and urban? = 0 and fitness = 1 and population > 5]
             if any? development_patch 
                [let selected_patch one-of development_patch
                 ask selected_patch [set urban? 1
                                     set land-use "Urban"
                                     set pcolor blue  
                                    ]
               ]
            ]

tick
end

I randomly chose one of the item to run, but the result shows it runs a bunch of items. So, how should I just let one of the patches (selected_patch) change color in each tick? Thanks.

Answer 1

Your issue stems from selecting your item inside a ask patches[...] call. This means that every single patch selects a patch that has to be turned blue. Moving the statement outside of the brackets fixes your issue

ask patches [ 
   set potential new-potential
   set development_patch patches with [potential > threshold and urban? = 0 and fitness = 1 and population > 5]
]

if any? development_patch [
     let selected_patch one-of development_patch
     ask selected_patch [
          set urban? 1
          set land-use "Urban"
          set pcolor blue  
     ]
]