javascript - 如何在 ES6 中使用 reduce() 来计算平均值？

Question

我正在尝试从 JSON 数据中提取 econ 和 season(请参见下面的屏幕截图)。我想找到每个季节的平均经济率

例如:季节 = 2018 经济率 = 10,20,30 所以平均经济率 = (10+20+30)/3 = 20

season = 2017 economy rate = 30,40,50 所以平均经济率 = (30+40+50)/3 = 40

所以我想计算特定赛季所有经济率的总和，然后取平均值，即用特定赛季的总和除以该赛季的比赛数。

下面是我尝试在 ES6 中使用 reduce() 的代码:

const economy = bowldata.reduce( (a,{season, econ})  => {
                    a[season] = a[season] + parseInt(econ);
                    return a; 
                }, {});
console.log(economy);

我正在获取 2018:NaN 但我希望我的输出为 2018:22 、2017: 50 等。即我想要该季节的键值对和平均经济率。

截图:

假设我有 JSON 数据:

var bowldata = [
    {
        season:2018
        economy:10
    },
    {   season:2018
        economy:20
    },
    {   season:2018
        economy:30
    },
    {   season:2017
        economy:40
    },
    {   season:2017
        economy:50
    },
    {   season:2016
        economy:10
    },
]

现在reduce()应该返回的对象是年份和平均经济率的键值对。

结果:[ 2018:20 , 2017:45 , 2016:10 ]

Answer 1

您可以将一个对象作为任何季节的默认值，因为您想要计算平均值。为此，您还需要计数。

var bowldata = [{ season: 2001, econ: '30' }, { season: 2001, econ: '40' }, { season: 2001, econ: '50' }, { season: 2001, econ: '60' }, { season: 2002, econ: '30' }, { season: 2002, econ: '40' }, { season: 2002, econ: '50' }, { season: 2003, econ: '60' }, { season: 2003, econ: '30' }, { season: 2003, econ: '40' }, { season: 2003, econ: '50' }, { season: 2003, econ: '60' }],
    economy = bowldata.reduce((a, { season, econ }) => {
        a[season] = a[season] || { sum: 0, count: 0 };
        a[season].sum += +econ;
        a[season].average = a[season].sum / ++a[season].count;
        return a;
    }, Object.create(null)),
    nice = Object.assign(...Object
        .entries(economy)
        .map(([k, { average }]) => ({ [k]: average }))
    );

console.log(nice);
console.log(economy);

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