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Lukschn
Lukschn

Reputation: 67

Netlogo making a list out of itself for a given length

I want to create a list out of its own values for a given length.

For example, given the list [0 1] and a desired list length of 7, the output would be [0 1 0 1 0 1 0]. The length is defined by population, and is defined by a slider. I declared the variable x that should iterate through the list. If the length of the list is shorter than the value of population it should be set to 0 again.

I tried it with a loop command but it runs infinitely:

let x 0
  loop[
    if length exp-dif-li <= population[
      ifelse x < length exp-dif-li[
        set x 0]
      [ set exp-dif-li lput item x exp-dif-li exp-dif-li
        set x x + 1]
    ]
  ]
]

Upvotes: 4

Views: 824

Answers (2)

Bryan Head
Bryan Head

Reputation: 12580

mod and n-values are your friends here:

to-report continue-list [ lst n ]
  report n-values n [ item (? mod length lst) lst ]
end

Example uses:

observer> show continue-list [0 1] 7
observer: [0 1 0 1 0 1 0]
observer> show continue-list [0 1] 1
observer: [0]
observer> show continue-list [0 1 2 3 4] 22
observer: [0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1 2 3 4 0 1]

Edit: Realized it would be good to talk about why this works! n-values n [ ... ] creates a list of length n by sending the numbers 0 through n - 1 to the given reporter. The reporter accesses the number with ? (this is the NetLogo task syntax). So we want to keep repeating the items in the original list. A really good function for repeatedly cycling through numbers is mod. In general, item i of the new list should be item i mod <length of original list>. So, putting that together, n-values n [ item (? mod length lst) lst ] creates a new list of length n by repeating the items from the list lst as necessary.

Upvotes: 5

King-Ink
King-Ink

Reputation: 2096

To get out of a loop you need to call end or stop.

inserting the line 

if length exp-dif-li = 7 [stop]

the right place would do it. Loop can very easily turn into a infinite loop and a freeze so it is best avoided.

I prefer while loops. they are safer and less prone to infinite loops which would look like this

while length exp-dif-li < 7
  [
   if length exp-dif-li <= population[
  ifelse x < length exp-dif-li[
    set x 0]
  [ set exp-dif-li lput item x exp-dif-li exp-dif-li
    set x x + 1]
  ]

Netlogo has another method which I have not seen elsewhere and is very robust against infinite loops. [repeat] the usage in you case would seem to be

  repeat 7  [
            if length exp-dif-li <= population[
             ifelse x < length exp-dif-li[set x 0]
             [ set exp-dif-li lput item x exp-dif-li exp-dif-li
            set x x + 1]
            ]

Upvotes: 1

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