按周或月进行计数和分组答案

【问题标题】：Do a count and group by weeks or months按周或月进行计数和分组
【发布时间】：2017-11-17 08:40:04
【问题描述】：

我有一个像这样的对象数组：

[ { date: '2017-11-17', count: 2 }, { date: '2017-11-16', count: 24 }, { date: '2017-11-15', count: 42 }, { date: '2017-11-14', count: 23 }, { date: '2017-11-13', count: 33 }, { date: '2017-11-12', count: 22 }, { date: '2017-11-11', count: 11 }, { date: '2017-10-04', count: 66 } ]

仅使用 momentJS 库和纯 javascript（没有 lodash _groupBy 等），我如何将结果分组并将“计数”加在一起，如下所示：

周分组：（星期一是一周的开始）

[ { date: '2017-11-13', count: 104 }, { date: '2017-11-06', count: 22 }, { date: '2017-10-02', count: 66 } ]

月份分组：（每月 1 号是月初）

[ { date: '2017-11-01', count: 26 }, { date: '2017-10-01', count: 66 } ]

谢谢。

【问题讨论】：

您有没有尝试过但没有成功？如果是，什么不起作用？您能否发布您尝试过的内容以及问题所在？
查看数组原型的map和reduce函数。 MDN 对此很有帮助。
stackoverflow.com/a/17861074/8281584，你看看这个链接吗
How can I group an array of objects by month?的可能重复

标签： javascript node.js momentjs

【解决方案1】：

以下代码按周分组。按月分组：

var datas = [ { date: '2017-11-17', count: 2 }, { date: '2017-11-16', count: 24 }, { date: '2017-11-15', count: 42 }, { date: '2017-11-14', count: 23 }, { date: '2017-11-13', count: 33 }, { date: '2017-11-12', count: 22 }, { date: '2017-11-11', count: 11 }, { date: '2017-10-04', count: 66 } ];
var groupedByWeek = datas.reduce((m, o) => {
    var monday = getMonday(new Date(o.date));
    var mondayYMD = monday.toISOString().slice(0,10);
    var found = m.find(e => e.date === mondayYMD);
    if (found) {
        found.count += o.count;
    } else {
        o.date = mondayYMD;
        m.push(o);
    }
    return m;
}, []);

console.log(groupedByWeek);

function getMonday(d) {
    var day = d.getDay();
    var diff = d.getDate() - day + (day === 0 ? -6 : 1);  
    return new Date(d.setDate(diff));
}

【讨论】：

【解决方案2】：

这是我写的一个函数。您将数组作为第一个参数传递，将“周”或“月”作为第二个参数传递。

function groupBy(elements, duration) {
  const formatted = elements.map(elem => {
    return { date: moment(elem.date).startOf(duration).format('YYYY-MM-DD'), count: elem.count }
  })

  const dates = formatted.map(elem => elem.date)
  const uniqueDates = dates.filter((date, index) => dates.indexOf(date) === index)

  return uniqueDates.map(date => {
    const count = formatted.filter(elem => elem.date === date).reduce((count, elem) => count + elem.count, 0)
    return { date, count }
  })
}

【讨论】：

【解决方案3】：

您可以使用分组函数和单个分组的回调（这里是月份），并使用哈希表来保持相同的组。

function groupBy(array, groupFn) {
    var hash = Object.create(null),
        result = [];

    array.forEach(function (o) {
        var key = groupFn(o);
        if (!hash[key]) {
            hash[key] = { date: key, count: 0 };
            result.push(hash[key]);
        }
        hash[key].count += o.count;
    });
    return result;
}

var data = [{ date: '2017-11-17', count: 2 }, { date: '2017-11-16', count: 24 }, { date: '2017-11-15', count: 42 }, { date: '2017-11-14', count: 23 }, { date: '2017-11-13', count: 33 }, { date: '2017-11-12', count: 22 }, { date: '2017-11-11', count: 11 }, { date: '2017-10-04', count: 66 }],
    month = function (o) { return o.date.slice(0, 7) + '-01'; },
    week = function (o) {
        var d = new Date(o.date),
            day = 1000 * 60 * 60 * 24,
            offset = 4 * day;

        d.setTime(Math.floor((d.valueOf() - offset) / 7 / day) * 7 * day + offset);
        return d.toISOString().slice(0, 10);
    };

console.log(groupBy(data, month));
console.log(groupBy(data, week));

.as-console-wrapper { max-height: 100% !important; top: 0; }

【讨论】：

【解决方案4】：

您可以使用array#reduce 使用对象查找将您的数据数组分组为月和周组。

const data = [ { date: '2017-11-17', count: 2 }, { date: '2017-11-16', count: 24 }, { date: '2017-11-15', count: 42 }, { date: '2017-11-14', count: 23 }, { date: '2017-11-13', count: 33 }, { date: '2017-11-12', count: 22 }, { date: '2017-11-11', count: 11 }, { date: '2017-10-04', count: 66 } ];

var sortedByMonth = data.reduce((res, {date, count}) => {
  let [year, month, day] = date.split('-');
  res[month] ? res[month].count += count : res[month] = { date : year+'-'+month+'-'+'01', count};
  return res;
},{});

console.log(Object.values(sortedByMonth));

var sortedByWeek = data.reduce((res, {date, count}) => {
  var startOfWeek = moment(date, 'YYYY-MM-DD').startOf('week').add(1,'days');
  res[startOfWeek] ? res[startOfWeek].count += count : res[startOfWeek] = {date: moment(startOfWeek).format('YYYY-MM-DD'), count};
  return res;
},{});
console.log(Object.values(sortedByWeek));

.as-console-wrapper { max-height: 100% !important; top: 0; }

&lt;script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.2/moment.min.js"&gt;&lt;/script&gt;

【讨论】：