How Navie Bayes works and Advantage and Disadvantages of Navie Bayes?

Data Science, AI and ML
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Working of Naïve Bayes’ Classifier can be understood with the help of the below example:

Suppose we have a dataset of weather conditions and corresponding target variable " Play ". So using this dataset we need to decide that whether we should play or not on a particular day according to the weather conditions. So to solve this problem, we need to follow the below steps:

  1. Convert the given dataset into frequency tables.
  2. Generate Likelihood table by finding the probabilities of given features.
  3. Now, use Bayes theorem to calculate the posterior probability.

Problem : If the weather is sunny, then the Player should play or not?

Solution : To solve this, first consider the below dataset:

Outlook Play
0 Rainy Yes
1 Sunny Yes
2 Overcast Yes
3 Overcast Yes
4 Sunny No
5 Rainy Yes
6 Sunny Yes
7 Overcast Yes
8 Rainy No
9 Sunny No
10 Sunny Yes
11 Rainy No
12 Overcast Yes
13 Overcast Yes

Frequency table for the Weather Conditions:

Weather Yes No
Overcast 5 0
Rainy 2 2
Sunny 3 2
Total 10 5

Likelihood table weather condition:

Weather No Yes
Overcast 0 5 5/14= 0.35
Rainy 2 2 4/14=0.29
Sunny 2 3 5/14=0.35
All 4/14=0.29 10/14=0.71

Applying Bayes’theorem:

*P(Yes|Sunny)= P(Sunny|Yes)P(Yes)/P(Sunny)

P(Sunny|Yes)= 3/10= 0.3

P(Sunny)= 0.35

P(Yes)=0.71

So P(Yes|Sunny) = 0.3*0.71/0.35= 0.60

*P(No|Sunny)= P(Sunny|No)P(No)/P(Sunny)

P(Sunny|NO)= 2/4=0.5

P(No)= 0.29

P(Sunny)= 0.35

So P(No|Sunny)= 0.5*0.29/0.35 = 0.41

So as we can see from the above calculation that P(Yes|Sunny)>P(No|Sunny)

Hence on a Sunny day, Player can play the game.

Advantages of Naïve Bayes Classifier:

  • Naïve Bayes is one of the fast and easy ML algorithms to predict a class of datasets.
  • It can be used for Binary as well as Multi-class Classifications.
  • It performs well in Multi-class predictions as compared to the other Algorithms.
  • It is the most popular choice for text classification problems .

Disadvantages of Naïve Bayes Classifier:

  • Naive Bayes assumes that all features are independent or unrelated, so it cannot learn the relationship between features.