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Weighted Randomness

Discussion in 'PHP' started by nevetS, Jul 14, 2005.

  1. #1
    I'm putting together a script, and I would like to implement weighted randomness, I believe similar to what the co-op does.

    essentially, I have 4 items to randomly select from. I would like item 1 to have a 50% probability of being selected, item 2 to have a 25% probability of being selected, item 3 a 15% probability of being selected and item 4 a 10% chance of being selected.

    Now, I can solve this problem by making an array of 100 items and populating 1 50 times, 2 25 times, 3 15 times, and 4 10 times, but there has to be a cleaner solution. I'm not sure what the memory requirements are, but it just seems like a waste to me.
    SEMrush
    Any ideas?
     
    nevetS, Jul 14, 2005 IP
    SEMrush
  2. Perrow

    Perrow Well-Known Member

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    #2
    Try something like this.

    X = random number between 0 and 100
    if x < 50 then choise = 1
    else if x < 75 then choise = 2
    else if x < 90 then choise = 3
    else choise = 4
    Code (markup):
    That should do the trick.
     
    Perrow, Jul 14, 2005 IP
  3. dct

    dct Finder of cool gadgets

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    #3
    If each object has a weight can you just do $RandNo = rand(1, totalweights); and then loop through your objects until $RandNo is within that objects range
    e.g.

    Item 1 - 1 -> 10 (weight 10)
    Item 2 - 11 -> 15 (weight 5)
    Item 3 - 16 -> 18 (weight 3)
    Item 4 - 19 -> 20 (weight 2)

    I don't think I've explained this very well but hopefully you'll get the gist, if you create a 100 element array I will never speak to you again :)
     
    dct, Jul 14, 2005 IP
  4. nevetS

    nevetS Evolving Dragon

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    #4
    I am sooo stupid sometimes. thanks guys. You have no idea the complexities that I was working my way through... :D
     
    nevetS, Jul 14, 2005 IP