Javascript/ES2015，计算出现的次数并存储为数组中的对象

Javascript/ES2015, count the number of occurrences and store as objects within an array

本文关键字：存储 数组 对象 ES2015 计算 Javascript      更新时间：2023-09-26

我正在从JSON提要中提取数据，并试图计算每个名称(name_class)发生的次数。

我想以以下格式返回一个对象数组，其中count指名称出现的次数:

myArray = [{name:"John", count: 5}, {name: "Sarah", count: 2}, {name: "Oliver", count: 3}];
到目前为止，我有以下内容，但这并不计算出现的次数，它只是向数组中添加另一个对象; 
   let namestUi = {
    renderNames(names){
        var counter2 = [];
        let namesFound = names.map((name) => {
          let {name_class} = name;
            if(counter2.name == name_class){
              counter2.count++;
            } else { counter2.push({name: name_class, count: 1}); }
        });
        console.log(counter2);
        return namesFound;
      }
    };

这是在构建对象数组，但不计算出现的次数。

function count(names){
    // Count occurrences using a map (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map)
    let map = new Map();
    for (let name of names) {
        map.set(name, (map.get(name) || 0) + 1);
    }
    // Transform to array of { name, count }
    let result = [];
    for (let [name, count] of map) {
        result.push({name: name, count: count});
    }
    return result;
}
count(["a", "b", "c", "a", "b", "a"])
// [{"name":"a","count":3},{"name":"b","count":2},{"name":"c","count":1}]

如何使用计数器变量存在一些问题。可以像访问普通对象一样访问属性，但将其定义为数组。而且你的map回调函数没有返回任何值。

你可以使用这段代码，它使用一个Map键计数器的名称，然后应用Array.from转换映射到一个数组的对象，如你所要求的:

let namestUi = {
    renderNames(names){
        return Array.from(
            names.reduce( (counters, {name_class}) =>
                counters.set(name_class, (counters.get(name_class) || 0) + 1),
                new Map() ),
            ([name, count]) => ({name, count})
        );
    }
};
let result = namestUi.renderNames([
    { name_class: "John" },
    { name_class: "John" },
    { name_class: "Frank" },
    { name_class: "John" },
]);
console.log(result);

相关文章：