Javascript/ES2015，计算出现次数并存储为数组中的对象

Question

我正在从 JSON 提要中提取数据，并尝试计算每个名称 (name_class) 出现的次数。

我想以以下格式返回一个对象数组，其中 count 是指名称出现的次数：

myArray = [{name:"John", count: 5}, {name: "Sarah", count: 2}, {name: "Oliver", count: 3}];

到目前为止，我有以下内容，但这不计算出现次数，它只是将另一个对象添加到数组中；

   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;
      }
    };

这是构建对象数组，但不计算出现次数。

Answer 1

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}]

Answer 2

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

您可以使用此代码，它使用Map来按名称键计数器，然后应用Array.from将该 Map 转换为您请求的对象数组：

 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);