globals [buttons]           ; Global variables
turtles-own [group]         ; Each turtle has "group" as a variable

to setup                    ; Initializes model for new run.
    set-default-shape turtles "circle" ; Turtles are circles
    clear-all                          ; Reset turtles and patches
    set buttons 500                    ; Set number of buttons to 500
    create-turtles (buttons)           ; Create "buttons" number of turtles
    ask turtles [setup-turtles]        ; Initialize each turtle
end

to setup-turtles            ; Called for each turtle during setup
    set group who                      ; Initialize "group" ins var to ID built-in
    setxy random screen-size-x random screen-size-y ; Set our x,y randomly
end

to go                       ; Step the model once
    locals [g1 g2]          ; This procedure has some temp local variables
    set g1 group-of turtle random buttons    ; g1 & g2 are two group values
    set g2 group-of turtle random buttons    ; chosen from two random turtles
    ask turtles [joinClusters g1 g2]   ; Merge group g1 with group g2
end

to joinClusters [g1 g2]     ; Convert group g1 turtles into g2 turtles
    if (group = g1) [set group g2 set color color-of turtle g2]
end