如何在具有重复属性名称的对象中获取最大属性值？

Question

假设我有一个具有以下值的数组：数组名称是“订阅者”1: {month: "2019-07-24", subs: 2}2: {month: "2019-07-31", subs: 3}3: {month: "2019-08-01", subs: 2}4: {month: "2019-08-02", subs: 3}5: {month: "2019-08-05", subs: 3}6: {month: "2019-08-08", subs: 4}7: {month: "2019-08-14", subs: 5}8: {month: "2019-08-20", subs: 7}9: {month: "2019-08-23", subs: 7}10: {month: "2019-08-28", subs: 8}11: {month: "2019-08-29", subs: 11}12: {month: "2019-09-02", subs: 2}13: {month: "2019-09-03", subs: 2}14: {month: "2019-09-04", subs: 3}15: {month: "2019-09-05", subs: 5}16: {month: "2019-09-06", subs: 5}17: {month: "2019-09-09", subs: 6}18: {month: "2019-09-10", subs: 7}19: {month: "2019-09-11", subs: 8}20: {month: "2019-09-12", subs: 9}我的问题是，我怎样才能按月获得最高的订阅量？预期输出：0: {month: "July", subs: 3}1: {month: "August", subs: 11}2: {month: "September", subs: 9}我尝试使用 array.map，但无法获得预期的输出。我也尝试使用 Math.max，但我似乎无法在对象中使用它。var getMonthlyValues = subscribers.map(value => {           var obj = {};        var dateName = new Date(value.period).toLocaleString('default', { month: 'long' });        obj = {month:dateName, subs:value.monthly}        return obj;    })我可以这样做，例如，如果这些来自数据库，列为月和子，以及它们各自的值。但是我怎么能在纯 JS 上做到这一点呢？

Answer 1

您可以取Map, 并收集subs每个的最大值month。

分步骤：

通过将 aMap作为累加器并以分组属性month为键来减少数组。作为值从先前存储的值或零和实际值中取最大值。

如果负值或零可用，请使用条件（三元）运算符?:，例如

  m.has(month) ? Math.max(m.get(month), subs) : subs

获取键/值对列表并返回具有自定义命名属性Array.from和映射函数的对象数组。

var data = [{ month: "July", subs: 2 }, { month: "July", subs: 3 }, { month: "August", subs: 2 }, { month: "August", subs: 3 }, { month: "August", subs: 3 }, { month: "August", subs: 4 }, { month: "August", subs: 5 }, { month: "August", subs: 7 }, { month: "August", subs: 7 }, { month: "August", subs: 8 }, { month: "August", subs: 11 }, { month: "September", subs: 2 }, { month: "September", subs: 2 }, { month: "September", subs: 3 }, { month: "September", subs: 5 }, { month: "September", subs: 5 }, { month: "September", subs: 6 }, { month: "September", subs: 7 }, { month: "September", subs: 8 }, { month: "September", subs: 9 }],

    result = Array.from(

        data.reduce(

            (m, { month, subs }) => m.set(month, Math.max(m.get(month) || 0, subs)),

            new Map

        ),

        ([month, subs]) => ({ month, subs })

    );

console.log(result);

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