如何计算数组的平均评分？

Question

下面给出了一个数组数据：

    const ratingData = [
        {name: 'St. Marys School', rating:5},
        {name: 'St. Zaviers School', rating:4},
        {name: 'St. Marys School', rating:3},
        {name: 'Rahul English Medium School', rating:2},
        {name: 'St. Francis High School', rating:3},
        {name: 'Rahul English Medium School', rating:1},
        {name: 'St. Francis High School', rating:4},
        {name: 'Mother Marys High School', rating:5}
    ];

在这个数组中，我想计算每个学校数据的平均评分。但问题是重复的条目，例如“St. Mary's School”有 2 个具有不同评级的条目。如何合并为一个并计算其平均评级？我尝试使用 map 函数，但对于每个条目，它都不起作用。

它的 o/p 应该看起来像这样。 （这只是一个例子）

const output = [
     { name: 'St. Marys School', averageRating: 4},
     { name: 'St. Zaviers School', averageRating: 4},
     { name: 'Rahul English Medium School', averageRating: 1.5},
     { name: 'St. Francis High School', averageRating: 3.5},
     { name: 'Mother Marys High School', averageRating: 5}
];

Answer 1

let ratingData = [
    {name: 'St. Marys School', rating:5},
    {name: 'St. Zaviers School', rating:4},
    {name: 'St. Marys School', rating:3},
    {name: 'Rahul English Medium School', rating:2},
    {name: 'St. Francis High School', rating:3},
    {name: 'Rahul English Medium School', rating:1},
    {name: 'St. Francis High School', rating:4},
    {name: 'Mother Marys High School', rating:5}
];

let sumData = {};

for (let element of ratingData) {
    if (sumData[element.name]) {
        sumData[element.name].sum = sumData[element.name].sum + element.rating;
        sumData[element.name].n++;
    } else {
        sumData[element.name] = {
            sum: element.rating,
            n: 1
        };
    }
}

console.log('sumData: ' + JSON.stringify(sumData));

let averageData = [];

for (let element of Object.keys(sumData)) {
    averageData.push({
        name: element,
        rating: sumData[element].sum / sumData[element].n
    });
}

console.log('averageData: ' + JSON.stringify(averageData));

sumData 将等于

{
    "St. Marys School": {
        "sum": 8,
        "n": 2
    },
    "St. Zaviers School": {
        "sum": 4,
        "n": 1
    },
    "Rahul English Medium School": {
        "sum": 3,
        "n": 2
    },
    "St. Francis High School": {
        "sum": 7,
        "n": 2
    },
    "Mother Marys High School": {
        "sum": 5,
        "n": 1
    }
}

平均数据将等于

[
    {
        "name": "St. Marys School",
        "rating": 4
    },
    {
        "name": "St. Zaviers School",
        "rating": 4
    },
    {
        "name": "Rahul English Medium School",
        "rating": 1.5
    },
    {
        "name": "St. Francis High School",
        "rating": 3.5
    },
    {
        "name": "Mother Marys High School",
        "rating": 5
    }
]

Answer 2

这是一个使用 reduce() 结合 Map 来检测重复条目的示例。

首先，它将原始数组缩减为 Map，该数组会累积数组中重复条目的评分。

{
{'St. Marys School': [5, 3, 1]},
{'St. Zaviers School': [4]},
...
}

然后我们使用Array.from 将这个Map 转换回一个数组，并将评级数组减少到一个平均值。

const ratingData = [
    {name: 'St. Marys School', rating:5},
    {name: 'St. Zaviers School', rating:4},
    {name: 'St. Marys School', rating:3},
    {name: 'Rahul English Medium School', rating:2},
    {name: 'St. Francis High School', rating:3},
    {name: 'Rahul English Medium School', rating:1},
    {name: 'St. Francis High School', rating:4},
    {name: 'Mother Marys High School', rating:5},
    {name: 'St. Marys School', rating:1}
    ]
    
const mapData = ratingData.reduce((acc, {name, rating}) => {
  const match = acc.get(name);
  match ? 
  match.push(rating) :
  acc.set(name, [rating]);
  return acc;
}, new Map);

const averageArray = Array.from(mapData, ([name, ratings]) => {
  const rating = ratings.reduce((a, r) => (a + r))/ratings.length;
  return { name, rating }
});

console.log(averageArray);