Question

我有一个包含日期的简单对象列表，我需要按日期对它们进行分组。不幸的是，它似乎无法发挥作用。

以下是简化代码：

games = [
    {date:"3/5/17", name:"game 1, 3"},
    {date:"3/5/17", name:"game 2, 3"},
    {date:"4/5/17", name:"game 3, 4"},
    {date:"4/5/17", name:"game 4, 4"},
    {date:"4/5/17", name:"game 5, 4"},
    {date:"5/5/17", name:"game 6, 5"},
    {date:"5/5/17", name:"game 7, 5"},
]

let games_by_date = []

games.map( (i)=>{ 
    if(!games_by_date[i['date']]) 
    games_by_date[i['date']]=[]; 
  games_by_date[i['date']].push(i);
} )

console.log(games_by_date)     // shows [3/5/17: Array[2], 4/5/17: Array[3], 5/5/17: Array[2]], but shows it as Array[0]
console.log(games_by_date[0])  // undefined
console.log(games_by_date[1])  // undefined

games_by_date.map( (g)=>console.log(g) )  // doesn't even gets there

如果我这样做但使用不同的列，它就能正常工作。

＆＃13;

games = [
	{date:"3/5/17", day:"3", name:"game 1, 3"},
	{date:"3/5/17", day:"3", name:"game 2, 3"},
	{date:"4/5/17", day:"4", name:"game 3, 4"},
	{date:"4/5/17", day:"4", name:"game 4, 4"},
	{date:"4/5/17", day:"4", name:"game 5, 4"},
	{date:"5/5/17", day:"5", name:"game 6, 5"},
	{date:"5/5/17", day:"5", name:"game 7, 5"},
]

let games_by_date = []

games.map( (i)=>{ 
	if(!games_by_date[i['date']]) 
  	games_by_date[i['date']]=[]; 
  games_by_date[i['date']].push(i);
} )

console.log(games_by_date)
console.log(games_by_date[0])
console.log(games_by_date[1])

games_by_date.map( (g, d)=>console.log(d, g) )

console.log("--------------------")

let games_by_day = []

games.map( (i)=>{ 
	if(!games_by_day[i['day']]) 
  	games_by_day[i['day']]=[]; 
  games_by_day[i['day']].push(i);
} )

console.log(games_by_day)
console.log(games_by_day[0])
console.log(games_by_day[1])

games_by_day.map( (g, d)=>console.log(d, g) )

＆＃13;

所以它似乎因为我使用的键的类型而发生。

你遇到过它，你是怎么解决的？感谢

Answer 1

您可以使用reduce来按键分组：

let games = [
    {date:"3/5/17", name:"game 1, 3"},
    {date:"3/5/17", name:"game 2, 3"},
    {date:"4/5/17", name:"game 3, 4"},
    {date:"4/5/17", name:"game 4, 4"},
    {date:"4/5/17", name:"game 5, 4"},
    {date:"5/5/17", name:"game 6, 5"},
    {date:"5/5/17", name:"game 7, 5"},
];

let games_by_date = games.reduce((a,b) => {
  a[b.date] = a[b.date] ? a[b.date].concat(b) : [b];
  return a;
}, {});

console.log(games_by_date);

因为“日期”只是字符串，所以它们应该没有问题。

正如@Liam指出的那样，这将创建一个对象而不是数组，有关此内容的完整说明，请参阅@Liam's answer。

Answer 2

您的games_by_date数组应该是一个能够按日期键入的对象。 day键自动转换为整数，因为它们是整数形式，因此可以用作数组中的键。但是，要使用日期字符串，您必须更改var games_by_date = {}并且它应该可以正常工作。

请注意，您不能.map常规JavaScript中的对象。但是，您可以使用for (i in games_by_date)循环键，或使用lodash提供_.map(object, callback)。

Javascript：使用日期作为数组键并不起作用

2 个答案: