[Fluxus] picking a function with weights

[evan.raskob [lists]]

The method I use is pretty similar, generating a random number based  
on the sum of the weights, then subtracting the weights from it in  
order until I hit (or go below) 0 which means the current weighted  
item should be selected.

Although I suppose you could use what Dave said with multiple list  
items, especially if you are just keeping track of integers, as they  
are easily duplicated without losing much memory.

  Cheers
Evan



On Feb 2, 2010, at 2:17 PM, Dave Griffiths wrote:

> Hi Kassen,
>
> Without weights:
>
> (define (choose l)
>  (list-ref l (random (length l))))
>
> (define funcs
>  (list
>   (lambda () (display "one"))
>   (lambda () (display "two"))
>   (lambda () (display "three"))
>   (lambda () (display "four"))
>   (lambda () (display "five"))))
>
> ((choose funcs))
>
> I generally do weighting by duplicating list elements, but there  
> must be
> a better way?
>
> cheers,
>
> dave
>
> On Tue, 2010-02-02 at 15:08 +0100, Kassen wrote:
>> Dear list,
>>
>>
>> Another -probably simple- Scheme question. Suppose we wanted to
>> execute one (and only one) of a few functions, pick this one randomly
>> and assign weights to them. For example we might like to populate a
>> world with mostly cubes, some spheres and just a few cylinders. How
>> would we go about this cleanly? I could nest a train of "if"
>> statements that would compare a (rndf) to a constant but that's  
>> hardly
>> convenient and leads to ugly code. I could also set up a few (cond)
>> statements to use with a single random number but since we are
>> basically dealing with picking from a list I could imagine Scheme,
>> which is specialised in lists, would have some specialised trick up
>> it's sleeve that might serve?
>>
>>
>> Yours,
>> Kas.
>