如何从嵌套数组中获取最后一项？

Question

我一直在努力从嵌套数组中获取最后一个对象项。我尝试实现了 flatMap、flat、filter 和 splice。但是，我仍然无法获得预期的数组。

const array = [
  [
    {
      total_cases: 18,
    },
    {
      total_cases: 32,
    },
    {
      total_cases: 7,
    },
  ],
  [
    {
      total_cases: 4,
    },
    {
      total_cases: 52,
    },
  ],
  [
    {
      total_cases: 68,
    },
  ],
];

我有一个像上面这样的数组。如何只将最后一个对象项放入新数组？

预期的新数组应该是这样的：

[7, 52, 68]

提前致谢！

Answer 1

根据对问题的更改编辑。

您可以使用 map and slice to select only the last element of each nested array, then flat 来展平数组并再次使用 map 到 select total_cases 值：

const array = [
  [ 
    { total_cases: 18 },
    { total_cases: 32 },
    { total_cases: 7 },
  ],
  [ 
    { total_cases: 4 },
    { total_cases: 52 },
  ],
  [ 
    { total_cases: 68 },
  ],
];

const result = array
  .map(a => a.slice(a.length - 1))
  .flat(1)
  .map(o => o.total_cases)
  
console.log(result)

原答案

您可以flatten the array, filter it based on the date value and then use map提取total_cases值：

const array = [
  [
    {
      date: "2020-02-25",
      total_cases: 18,
    },
    {
      date: "2020-02-26",
      total_cases: 32,
    },
    {
      date: "last-object",
      total_cases: 7,
    },
  ],
  [
    {
      date: "2020-02-26",
      total_cases: 4,
    },
    {
      date: "last-object",
      total_cases: 52,
    },
  ],
  [
    {
      date: "last-object",
      total_cases: 68,
    },
  ],
];

const result = array
  .flat(1)
  .filter(o => o.date == 'last-object')
  .map(o => o.total_cases)
  
console.log(result)

Answer 2

您可以使用.at()方法。负参数从数组中的最后一项开始倒数。所以 .at(-1) return 最后一个数组的元素。

const array=[[{total_cases:18},{total_cases:32},{total_cases:7}],[{total_cases:4},{total_cases:52}],[{total_cases:68}]];

const result = array.map(e => e.at(-1).total_cases);

console.log(...result);

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如何从嵌套数组中获取最后一项？

How can I get the last items from a nested array?

javascript

arrays

object

nested