calculate 5 star ratings in js array of object-CodePudding

I have an array that consist of feedback objects. Each object is a user feedback left for a product:

Array [ {…}, {…} ]
0: Object { id: "1223", quality: 3, material: 4, … }
1: Object { id: "7342", quality: 3, material: 5, … }
...

Users can leave feedback for each category quality, material, ... out of 5.

I want to use the weighted average so on my site, I can show for example:

quality: 3
material: 4

This is weighted average calculated by this formula:

quality: (5*0   4*0   3*2   2*0   1*0) / (2) = 3
material: (5*1   4*0   3*1   2*0   1*0) / (2) = 4

I want to add this my js project, so I loop through all feedback:

const total = []
const feedback = [{
    id: "1223",
    quality: 3,
    material: 4,
  },
  {
    id: "7342",
    quality: 3,
    material: 5,
  }
];
feedback.forEach(function(arrayItem) {
  const score = arrayItem.quality
  total.push(score)
})
console.log(total.reduce((partialSum, a) => partialSum   a, 0))

I am confused about how to do the calculation for each star, for example to get number of 1s, 2s, 3s, 4s, and 5 starts. How can I modify my code to return the rating result?

CodePudding user response：

You could collect all sums in an object and calculate the aveage on the fly.

If you need an array, take only the values.

const
    feedback = [{ id: "1223", quality: 3, material: 4 }, { id: "7342", quality: 3, material: 5 }],
    types = ['quality', 'material'],
    result = feedback.reduce((r, o) => {
        types.forEach(type => {
            r[type] ??= { type, total: 0, count: 0 };
            r[type].total  = o[type];
            r[type].avarage = r[type].total /   r[type].count;
        });
        return r;
    }, {});

console.log(result);
console.log(Object.values(result));

.as-console-wrapper { max-height: 100% !important; top: 0; }

CodePudding user response：

By changing the total variable from an array to an integer, we can add up the values first, and then divide them by the number of items in feedback to obtain the average rating.

const feedback = [{
    id: "1223",
    quality: 3,
    material: 4,
  },
  {
    id: "7342",
    quality: 3,
    material: 5,
  }
];

let totalQuality = 0;
let totalMaterial = 0;
feedback.forEach(function(arrayItem) {
    totalQuality  = arrayItem.quality;
    totalMaterial  = arrayItem.material;
})
let avgQuality = totalQuality / feedback.length;
let avgMaterial = totalMaterial / feedback.length;
console.log(avgQuality);
console.log(avgMaterial);