Javascript:使用日期作为数组键不起作用

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，它似乎不起作用。

这是简化的代码:

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

如果我执行相同操作但使用不同的列，则它可以正常工作。

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) )

所以这似乎是由于我使用的 key 类型而发生的。

您遇到过这个问题吗？您是如何解决的？谢谢

Answer 1

您可以使用reduce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);

由于“日期”只是字符串，因此它们应该不会有问题。

正如 @Liam 正确指出的那样，这将创建一个对象而不是数组，有关此问题的完整说明请参阅 @Liam's answer 。