Subtract. SET variableX-variableY only once

Question

I'm trying to set a resource variable. It will be time and will function like sugar in sugarscape. Its setup is: ask agentes [set time random-in-range 1 6]. The thing is... I want the agentesto participate in activities linking like we said here. But, with each participation, it should subtract a unity of agentes's time. I imagine it must be with foreachbut I seem to be unable to grasp how this works.

  ask n-of n-to-link agentes with [n-t-activity = [n-t-activity] of myself] in-radius sight-radius [
    while [time >= 2] [
      create-participation-with myself [ set color [color] of myself ] ]
      foreach (command I don't know)[
        set time time - count participations]]

Essentially, I want the agentes to look if they have time to participate. If they do, they create the link and subtract 1 to their time. Only ONE per participation. If they have 3 time, they'll have 2 participations and 1 time. If they have 1 time, they won't have links at all.

EDIT You're right. I don't need while. About foreach, every place I looked said the same thing but I can't think of other way. About colors, they're only for show purpose. The relationship between time and participation counts is as follows: the agentes have time they can spend in activities. They participate if time>=2. But every participation (link with activity) consumes 1 time when the link is active (I didn't write the decay code yet; they'll regain their time when it is off).

EDIT V2

Nothing, it keeps subtracting even with the []. Maybe the best choice is if I give you the code so you can try it. You'll have to set 5 sliders: prob-female (53%), initial-people (around 200), num-activity (around 20), n-capacity (around 25) and sight-radius (around 7). And two buttons, setup and go. I also set a patch size of 10 with 30 max-pxcor and max-pycor. Here is the code. Sorry if I'm not clear enough!

undirected-link-breed [participations participation]

turtles-own [
  n-t-activity
]

breed [activities activity]
activities-own [
  t-culture-tags
  shared-culture
]

breed [agentes agente]
agentes-own [
  gender
  time
  culture-tags
  shared-culture
]

to setup
  clear-all
  setup-world
  setup-people-quotes
  setup-activities
  reset-ticks
END

to setup-world
  ask patches [set pcolor white]
END

to setup-people-quotes                                                      
  let quote (prob-female / 100 * initial-people)                            
  create-agentes initial-people
      [ while [any? other turtles-here ]
      [ setxy random-xcor random-ycor ]
      set gender "male" set color black
  ]
  ask n-of quote agentes
    [ set gender "female" set color blue
  ]
  ask agentes [
    set culture-tags n-values 11 [random 2]
        set shared-culture (filter [ i -> i = 0 ] culture-tags)
  ]
  ask agentes [
    set time random-in-range 1 6
  ]
  ask agentes [
    assign-n-t-activity
  ]
END

to setup-activities
  create-activities num-activity [
    set shape "box"
    set size 2
    set xcor random-xcor
    set ycor random-ycor
    ask activities [
      set t-culture-tags n-values 11 [random 2]
      set shared-culture (filter [i -> i = 0] t-culture-tags)
    ]
    ask activities [
      assign-n-t-activity]
  ]
END

to assign-n-t-activity                                                      
  if length shared-culture <= 4 [
    set n-t-activity ["red"]
    set color red
  ]
  if length shared-culture = 5 [
    set n-t-activity ["green"]
    set color green
  ]
  if length shared-culture = 6 [
    set n-t-activity ["green"]
    set color green
  ]
  if length shared-culture >= 7 [
    set n-t-activity ["black"]
    set color black
  ]
END

to go
  move-agentes
  participate
  tick
end

to move-agentes
  ask agentes [
    if time >= 2 [
    rt random 40
    lt random 40
    fd 0.3
  ]
  ]
end

to participate
  ask activities [
   if count my-links < n-capacity [
      let n-to-link ( n-capacity - count my-links)
      let n-agentes-in-radius count (
        agentes with [
          n-t-activity = [n-t-activity] of myself ] in-radius sight-radius)
      if n-agentes-in-radius < n-to-link [
        set n-to-link n-agentes-in-radius
      ]
      ask n-of n-to-link agentes with [
        n-t-activity = [n-t-activity] of myself] in-radius sight-radius [
        if time >= 2 [
          create-participation-with myself [
            set color [color] of myself ]
          ask agentes [set time time - count my-participations] ]
        ]
      ask activities [
        if not any? agentes in-radius sight-radius [
          ask participations [die]
          ]
        ]
      ]
    ]
end

to-report random-in-range [low high]
  report low + random (high - low + 1)
END

EDIT V3

I asked Bill Rand to help me and he solved the problem. The issue was in this line: let candidates agentes with [ n-t-activity = [n-t-activity] of myself ] in-radius sight-radius. He solved the problem this way: let candidates agentes with [ n-t-activity = [n-t-activity] of myself and not participation-neighbor? myself ] in-radius sight-radius. Being this and not participation-neighbor? myself the condition to make sure that the agente is not already a part of that activity.

Answer 1

You almost never need foreach in NetLogo. If you find yourself thinking you need foreach, your immediate reaction should be that you need ask. In particular, if you are iterating through a group of agents, this is what ask does and you should only be using foreach when you need to iterate through a list (and that list should be something other than agents). Looking at your code, you probably don't want the while loop either.

UPDATED FOR COMMENTS and code - you definitely do not need while or foreach. Your problem is the following code. You ask agentes that satisfy your conditions to create the links, but then you ask ALL AGENTES to change their time (line I have marked), not just the agentes that are creating participation links.

  ask n-of n-to-link agentes with [
    n-t-activity = [n-t-activity] of myself] in-radius sight-radius [
    if time >= 2 [
      create-participation-with myself [
        set color [color] of myself ]
      ask agentes [set time time - count my-participations] ]    ; THIS LINE
    ]

The following code fixes this problem. I have also done something else to simplify reading and also make the code more efficient - I created an agentset (called candidates) of the agentes that satisfy the conditions. In this code, the candidates set is only created once (for each activity) instead of twice (for each activity) because you are creating it to count it and then creating it again to use for participation link generation.

to participate
  ask activities
   [ if count my-links < n-capacity
     [ let candidates agentes with [ 
           n-t-activity = [n-t-activity] of myself ] in-radius sight-radius
        let n-to-link min (list (n-capacity - count my-links) (count candidates ) )
        ask n-of n-to-link candidates
        [ if time >= 2
          [ create-participation-with myself [ set color [color] of myself ]
            set time time - count my-participations ]    ; REPLACED WITH THIS LINE
        ]
      ask activities [
        if not any? agentes in-radius sight-radius [
          ask participations [die]
          ]
        ]
      ]
    ]
end