[Solved] Suggestions on randoming - Page 2

Airkish · 07-14-2018 , 16:57 Re: Suggestions on randoming

Quote:

Originally Posted by KliPPy

You could map your probabilities so they all add up to a total of 1, whatever their values are. I'll be expressing probabilities in the range [0, 1] but you can always multiply it by 100 to display the chance in percents.

Untested, but the same algorithm did work in JavaScript for me:

Code:

GetRandomItem(const Float:itemChances[], count = sizeof itemChances) {
	new Array:mappedChances = ArrayCreate(1, 0);
	new index = 0;
	new Float:sum = 0.0;
	
#if AMXX_VERSION_NUM > 182
	ArrayResize(mappedChances, count);
#endif

	// Put all elements into mappedChances and accumulate
	for(index = 0; index < count; index++) {
		ArrayPushCell(mappedChances, itemChances[index]);
		sum += itemChances[index];
	}
	// Map so the sum of all chances is 1
	for(index = 0; index < count; index++) {
		ArraySetCell(mappedChances, index, ArrayGetCell(mappedChances, index) / sum);
	}
	sum = 0.0;
	new const Float:rand = random_float(0.0, 1.0);
	for(index = 0; index < count; index++) {
		sum += ArrayGetCell(mappedChances, index);
		if(rand <= sum) {
			break;
		}
	}
	
	ArrayDestroy(mappedChances);
	return index;
}

Code:

new const Float:itemChances[] = { 0.5, 0.1, 0.05, 0.15, 0.2, 0.4, 0.04, 0.06, 0.5 };
new const result = GetRandomItem(itemChances, sizeof itemChances);

As you can see, the chances in the array add up to 2.0 (or 200% percent), but in that case if you divide them by 2 they will add up to 1.0.
It's pretty much what Fysiks did but with the mapping step so input values don't have to add up to 100%.

It always return first number from array

fysiks · *Last edited by fysiks; 07-14-2018 at 18:32.*

Quote:

Originally Posted by KliPPy

As you can see, the chances in the array add up to 2.0 (or 200% percent), but in that case if you divide them by 2 they will add up to 1.0.
It's pretty much what Fysiks did but with the mapping step so input values don't have to add up to 100%.

Well, I assumed that adding up to 100 was a trivial task which is should be.

If you don't want to do the math beforehand, you can simply replace

Code:

rand = random(100)

with

Code:

	i = sum = 0
	for( i = 0; i < count; i++ )
	{
		sum += itemChances[i]
	}
	rand = random(sum)

But realize that if they don't add up to 100, the values basically have no meaning, they're just arbitrary. Though, I can think of some minor use cases to do this to reduce the amount of math required to adjust probabilities.

Quote:

Originally Posted by Airkish

It always return first number from array

Did you even try mine? It's super simple and it works. You can play around with the numbers to get what you need. If you don't know how to do the adding up to 100 thing, you can do the code replacement I mentioned above. It will be more efficient than Klippy's function.

Airkish · 07-15-2018 , 04:11 Re: Suggestions on randoming

Thanks everyone for help, solved using fysiks suggestions.