algorithm used to calculate 5 star ratings

Question

I need to calculate 5-star ratings like the one on Amazon website. I have done enough search to find what is the best algorithm, but I am not able to get a proper answer. For ex

Answer 1

You may want to check this algorithm out: Calculating Average Rating the Right Way using PHP and MySQL - there's no need of saving each "star" (aka rating grade) and its corresponding number of votes and then having to retrieve thousands of rows from the database every time you need to calculate their average. (unless you want to display exactly how many people rated the given item with 1, 2, 3, 4 & 5 stars)

Answer 2

According to your question your solution will be like this.

Sum of (Rate*TotalRatingOfThatRate)/ TotalNumberOfReviews

((5*252)+(4*124)+(3*40)+(2*29)+(1*33)) / (252+124+40+29+33)

output will be 4.1

Answer 3

In addition, I am just trying to make practical and full code for all.

My Json Object Array

var yourRatingData =[{
        review_id:1,
        customer_id:5,
        customer_name:"Faysal",
        rating:5,
        review_content:"I like this product it's cool and best in quality"
    },
    {
        review_id:2,
        customer_id:6,
        customer_name:"Adams",
        rating:4,
        review_content:"It's quality product though price a bit high"
    },
    {
        review_id:3,
        customer_id:8,
        customer_name:"Jane",
        rating:3,
        review_content:"I like but should improve quality"
    },
    {
        review_id:4,
        customer_id:9,
        customer_name:"Julia",
        rating:1,
        review_content:"It's not good"
    }];

Rating Calculation

let _5star = yourRatingData.filter(r=>r.rating==5).length;
let _4star = yourRatingData.filter(r=>r.rating==4).length;
let _3star = yourRatingData.filter(r=>r.rating==3).length;
let _2star = yourRatingData.filter(r=>r.rating==2).length;
let _1star = yourRatingData.filter(r=>r.rating==1).length;

//Sum of individual star.
let sumOfRating = parseInt( _5star + _4star + _3star + _2star + _1star );

//Total number of rating
let overallRating = parseInt( 5*_5star + 4*_4star + 3*_3star + 2*_2star +1*_1star );

//Average of all rating
let averageRating = parseFloat(overallRating/sumOfRating);

//Percentage of each star rating
let _5starPercentage = parseInt((_5star/totalRating)*100);
let _4starPercentage = parseInt((_4star/totalRating)*100);
let _3starPercentage = parseInt((_3star/totalRating)*100);
let _2starPercentage = parseInt((_2star/totalRating)*100);
let _1starPercentage = parseInt((_1star/totalRating)*100);

I think it's helpful.

Answer 4

Weighted average, sum the number of stars times its weight, and then divide it through by the total number of reviews.

Answer 5

(Total nunber of star / total number of persons who review * 5 ) * 5

= Answer

Fixed decimals in js to 1.

answer.toFixed(1);

Example the total reviews of 5 person is 20 star.

(20/5*5)*5 = 4.0

Answer 6

Yes, you can average them out:

(5 * 252 + 4 * 124 + 3 * 40 + 2 * 29 + 1 * 33) / 478 = 4.11