[PD] Weighted Randomness

Mathieu Bouchard matju at artengine.ca
Fri Oct 12 20:07:42 CEST 2007

On Fri, 12 Oct 2007, B. Bogart wrote:

> Does someone have a very simple implementation of a weighted randomness
> patch where the distribution of the numbers is read from a table? I see
> Miller's moses example, but I would like more graphic control of density.

First, the sum all the weights should be 1. If it doesn't, or if you 
don't know in advance, sum all the weights.

Then build a second table, in which each element is the sum all 
(inclusively) previous elements of the first table. This is the sum of the 
previous element of the second table and the current element of the first 
table. This second table is the cumulative distribution.

Then generate a random number between 0 included and the sum of all 
weights excluded. Finally, scan the table from 0 upwards until you hit any 
number above the random number. That index is the output value.

You don't absolutely need the second table, but it does save a bit of time 

If ever you need a much larger table, then it may become too slow, and if 
so, then write again and I'll explain how to accelerate it.

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| Mathieu Bouchard - tél:+1.514.383.3801, Montréal QC Canada

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