The Ultimate Probability Controller Script for Games in Unity

ProbabilitiesController.cs

//Full Youtube Tutorial on this Script: https://youtu.be/84rs2Q0z9ak
//The script doesn't have any kind of Input Validation you should added to the lists before calling the functions

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ProbabilitiesController : MonoBehaviour
{
    #region Basic Probability check

    //this is the basic Probability function that will take the item chance is 30% and then check if you'll get or not
    public bool ProbabilityCheck(int itemProbability)
    {
        float rnd = Random.Range(1, 101);
        if (rnd <= itemProbability)
            return true;
        else
            return false;
    }
    #endregion

    #region Normal items Probability from 100

    List<float> cumulativeProbability;
    
    //This function is called with the Item probability array and it'll return the index of the item
    // for example the list can look like [10,25,30] so the first item has 10% of showing and next one has 25% and so on
    public int GetItemByProbability(List<float> probability) //[50,10,20,20]
    {
        //if your game will use this a lot of time it is best to build the arry just one time
        //and remove this function from here.
        if(!MakeCumulativeProbability(probability))
            return -1; //when it return false then the list excceded 100 in the last index

        float rnd = Random.Range(1, 101); //Get a random number between 0 and 100

        for (int i = 0; i < probability.Count; i++)
        {
            if (rnd <= cumulativeProbability[i]) //if the probility reach the correct sum
            {
                return i; //return the item index that has been chosen 
            }
        }
        return -1; //return -1 if some error happens
    }
    
    //this function creates the cumulative list
    bool MakeCumulativeProbability(List<float> probability)
    {
        float probabilitiesSum = 0;

        cumulativeProbability = new List<float>(); //reset the Array

        for (int i = 0; i < probability.Count; i++)
        {
            probabilitiesSum += probability[i]; //add the probability to the sum
            cumulativeProbability.Add(probabilitiesSum); //add the new sum to the list
            
             //All Probabilities need to be under 100% or it'll throw an exception
            if (probabilitiesSum > 100f)
                {
                    Debug.LogError("Probabilities exceed 100%");
                    return false;
                }
        }
        return true;
    }

    #endregion

    #region Normal items Probability By Rarity
    List<float> cumulativeByRarity;

    //This function is called with the Item probability array and it'll return the index of the item
    // for example the list can look like [10,25,30] so the first item has 10% of showing and next one has 25% and so on
    public int GetItemByProbabilityRarity(List<float> probabilityRarity)
    {
        //if your game will use this a lot of time it is best to build the arry just one time
        //and remove this function from here.
        MakeCumulativeByProbabilityRarity(probabilityRarity);

        float rnd = Random.Range(1, 101); //Get a random number between 0 and 100

        for (int i = 0; i < probabilityRarity.Count; i++)
        {
            if (rnd <= cumulativeByRarity[i]) //if the probility reach the correct sum
            {
                return i; //return the item index that has been chosen 
            }
        }
        return -1; //return -1 if some error happens
    }
    
    
    //this function creates the cumulative list
    void MakeCumulativeByProbabilityRarity(List<float> probabilityRarity)
    {
        float probabilitiesSum = 0;

        cumulativeByRarity = new List<float>(); //reset the Array

        float ProbilityModifier = GetprobabilityByRarityModifer(probabilityRarity);

        for (int i = 0; i < probabilityRarity.Count; i++)
        {
            probabilitiesSum += probabilityRarity[i] * ProbilityModifier; //add the probability to the sum
            cumulativeByRarity.Add(probabilitiesSum); //add the new sum to the list
        }

        //No need to check if it's bigger than 100 because it'll always be 100 max
    }

    //This function is used to get a modifer to be able to get the probabilityRarity List to fit in the cumulativeByRarity list from 0 to 100
    float GetprobabilityByRarityModifer(List<float> probabilityRarity) // 5 , 20 , 2
    {
        float itemRaritySum = 0;

        for (int i = 0; i < probabilityRarity.Count; i++)
            itemRaritySum += probabilityRarity[i];

        return 100 / itemRaritySum;
    }

    #endregion

    #region Normal Probability Num In Num

    //This Function will return true if the item is lucky enough to be picked by a small chance of one in something
    //and 100% chance to get the item if its 1 in 1 ... XD
    public bool OneInProbability(int In)
    {
        float rnd = Random.Range(1, In + 1);
        if (rnd <= 1)
            return true;
        else
            return false;
    }

    //This Function will return true if the item is lucky enough to be picked by a small chance of num in something
    //This can be used instead the first one without passing the second variable
    public bool ChanceInProbability(int In, int chance = 1)
    {
        float rnd = Random.Range(1, In + 1);
        if (rnd <= chance)
            return true;
        else
            return false;
    }
    #endregion
}