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#1
April 22nd, 2007, 04:57 PM
 techwiz18
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Function which returns true with a given probability

I need to create a function which returns true with a given probability. For example:

foo(.1) returns true with probability .1

Could someone provide either a ruby implementation or a generic way to do this?

#2
April 24th, 2007, 09:23 AM
 crownjewel82
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Code:
public boolean foo(double probability) {
return true;
}

Seriously, You've got to specify some more logical requirements than that.
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#3
April 26th, 2007, 03:47 AM
 techwiz18
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I've said plenty. The technical term for what I have described is weighted random selection. In this case, the selection is between two elements: true and false. The probability p, given as an argument, is the weight assigned to true, and therefore the weight assigned to false is 1-p.

I ended up finding a Ruby implementation of weighted random selection that works for any number of elements; using this, I wrote my function.

#4
April 26th, 2007, 12:13 PM
Kage Bunshin

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Its one of those things you have to read twice. Trust me, he isn't usually so "out-of-it". Also, welcome to Dev Shed =D
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#5
April 26th, 2007, 05:18 PM
 techwiz18
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Quote:
 Its one of those things you have to read twice.

Agreed. Also, I probably could have done better job explaining what I was looking for.

#6
April 26th, 2007, 06:58 PM
 Oler1s
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Use a PRNG.

Say you take a probability out of 100. So for foo(.1), that's really like saying, I have a random number from 1-100. Is it less than 10? A standard PRNG available in most languages gives you a uniform distribution, so the probability is .1 that the number is less than 10. So look up creating random numbers in Ruby.

Generate random number within a range (something like 1-100, 1-1000). Check if random number is less than probability*range. If it is, return true, otherwise return false.
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