In english, what you might want to do, is set boundaries. Let's choose difficult numbers to drive the point.

Let's say you can easily generate a number between 0 and 5. Let's say you want to choose from the set (0,1,2,3) with weights (10,30,12,44).

First, add up your weights. You'll get your fractions that way. 10/96, 30/96 etc etc.. Now find the distance between your numbers. 0->5 is 5 integers long.

Now you wanna distribute, as floats, 0-5 to map to your set. You start with 0. 10/96 of 5 is 50/96. So 1 maps to \[0->50/96]. Now add your second boundary. 30/96 of 5 is 150/96. [50/96,150/96] is your second boundary. All I'm doing is finding the factions of the range (weights/whole * range of random numbers).

Now choose a random number betwe 0 and 5. It'll generate something in between one of those ranges.

[0,50/96) => 1,
[50/96,150/96) => 2,
on and on
[some fraction,5] => 3
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Divide your range of random numbers into fractions proportioned by the weights.

Here's a simple example. Say you could generate a number between 0 and 3, and your weights mapped like (1,2) with weights (1,2) respectively...

a random number between 0 and 3 would map like this

[0,3/3 * 3)  => 1
[3/3 * 3, 3/3*3 + 2/3*3 ) => 2

or...

[0,1] => 1,
[1,3] => 2
[download]

Find a random number bewtween 0 and 3.. p00f!

edited: Fri Mar 14 23:34:05 2003 by jeffa - formatting