Question

我有一个对象：

{
    name: 'xxx',
    date: '2016-01-01',
    value: 'xxx'
},
{
    name: 'xxx',
    date: '2016-01-02',
    value: 'xxx'
},
{
    name: 'xxx',
    date: '2016-01-01',
    value: 'xxx'
},
{
    name: 'xxx',
    date: '2016-01-03',
    value: 'xxx'
}

我想打印按周排序的值，每天只打印一个值，例如

This week:
- xxx from '2016.01.01'
- xxx from '2016.01.02'
- xxx from '2016.01.03'
Last week:
no values this week

等...

您是否知道如何正确实现这一目标？

我使用的是角度2和打字稿

Answer 1

一步一步：

输入您的商品→Item （可选但简化后续步骤）
获取getWeek()功能（Chrome支持，但非正式）
使用Map Map作为reduce()电话的种子，按周和日期收集项目

代码示例：（name已被删除以简化代码）

type Item = { date: string; value: string; };

const items: Item[] = [{
date: '2016-01-01',
value: 'foo'
},
{
date: '2016-01-01',
value: 'foo2'
},
{
date: '2016-01-02',
value: 'bar'
},
{
date: '2016-02-01',
value: 'baz'
},
{
date: '2016-03-01',
value: 'lol'
}];

// Source: https://weeknumber.net/how-to/javascript
const getWeek = function (date: Date) {
    date.setHours(0, 0, 0, 0);
    // Thursday in current week decides the year.
    date.setDate(date.getDate() + 3 - (date.getDay() + 6) % 7);
    // January 4 is always in week 1.
    var week1 = new Date(date.getFullYear(), 0, 4);
    // Adjust to Thursday in week 1 and count number of weeks from date to week1.
    return 1 + Math.round(((date.getTime() - week1.getTime()) / 86400000
        - 3 + (week1.getDay() + 6) % 7) / 7);
};

const itemsByWeek = items.reduce(
    (map: Map<string, Map<string, Item[]>>, item: Item) => {
        const [year, month, day] = item.date.split('-').map(x => +x);
        const date = new Date(year, month, day);
        const week = `${year}-${getWeek(date)}`;
        let weekGroup = map.get(week);
        if (!weekGroup) {
            weekGroup = new Map([[item.date, [item]]]);
            map.set(week, weekGroup);
        } else {
            const dayGroup = weekGroup.get(item.date);
            if (!dayGroup) {
                weekGroup.set(item.date, [item]);
            } else {
                dayGroup.push(item);
            }
        }
        return map;
    },
    new Map<string, Map<string, Item[]>>());

const concertMapToKeyValueArray = <K, V>(map: Map<K, V>) => {
    return Array.from(map.entries()).map(tuple => {
        const [key, value] = tuple;
        return { key, value };
    });
};

concertMapToKeyValueArray(itemsByWeek)
    .forEach(weekGroup => {
        console.log(`Week: ${weekGroup.key}`);
        concertMapToKeyValueArray(weekGroup.value)
            .forEach(dayGroup => console.log(`- Date: ${dayGroup.key}, ` +
                `Values: [${dayGroup.value.map(item => item.value).join(', ')}]`));
    });

控制台中的输出：

Week: 2016-5
- Date: 2016-01-01, Values: [foo, foo2]
- Date: 2016-01-02, Values: [bar]
Week: 2016-9
- Date: 2016-02-01, Values: [baz]
Week: 2016-13
- Date: 2016-03-01, Values: [lol]

如何迭代对象并按周分组结果？

1 个答案: