[Solved] Suggestions on randoming

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