JavaScript：一种从数组中提取每第 5 项的更好方法

Question

我有一个坐标元组数组，例如

[ [ 1, 1 ],
  [ 2, 2 ],
  [ 3, 3 ],
  [ 4, 4 ],
  [ 5, 5 ],
  [ 6, 6 ],
  [ 7, 7 ],
  [ 8, 8 ],
  [ 9, 9 ],
  [ 10, 10 ]
  ...

我想从中提取每 5 个坐标到一个新数组中

这是我的实现

const coordinates = Array.from({ length: 30 }, (_, i) => [i + 1, i + 1])

const { filteredCoordinates } = coordinates.reduce(
  (accu, currCoordinate) => {
    if (accu.count === 5) {
      accu.filteredCoordinates.push(currCoordinate)
      accu.count = 1
    } else {
      accu.count += 1
    }
    return accu
  },
  {
    count: 1,
    filteredCoordinates: [],
  }
)

console.log(filteredCoordinates);

这很好用，但我想知道是否有更好的方法来做到这一点？

Answer 1

您可以根据给定索引的五的模来过滤数组。

const coordinates = Array.from({ length: 30 }, (_, i) => [i + 1, i + 1])

const everyFithCoordinate = coordinates.filter((_, i) => (i+1) % 5 === 0);

console.log(everyFithCoordinate);

Answer 2

您可以获取一个索引并将其递增所需的计数。

这种方法不会迭代整个数组，只会迭代所需的索引。

const
    coordinates = Array.from({ length: 30 }, (_, i) => [i + 1, i + 1]),
    filtered = [];

for (let i = 4; i < coordinates.length; i += 5) filtered.push(coordinates[i]);

console.log(filtered);

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

Answer 3

不需要完全循环，你可以使用传统的for循环并用step递增，即5

const coordinates = Array.from({ length: 30 }, (_, i) => [i + 1, i + 1]);

const result = [];
const step = 5;
for (let i = step - 1; i < coordinates.length; i += step) {
  result.push(coordinates[i]);
}

console.log(result);

/* This is not a part of answer. It is just to give the output full height. So IGNORE IT */
.as-console-wrapper { max-height: 100% !important; top: 0; }

Answer 4

I want to extract every 5th coordinates out of them into a new array

根据您对“提取”的定义，您可能希望将这些坐标从第一个数组移动到第二个数组。此示例使用 for statement. I cache the length, and then splice 输出数组中给定索引处的坐标，并将其推入新数组。然后减少长度和索引，因为它们在下一次迭代之前已经改变。

const coordinates = Array.from({ length: 32 }, (_, i) => [i + 1, i + 1]);

const out = [];
const count = 5;
let { length } = coordinates;

for (let i = count - 1; i < length; i += count) {
  out.push(coordinates.splice(i, 1)[0]);
  --length;
  --i;
}

console.log(JSON.stringify(out));
console.log(JSON.stringify(coordinates));

Answer 5

完成此任务的正确有效的功能方法是使用 Array.from()。但是据我所知，到目前为止还没有人正确实施它。试试吧

var coords = Array.from({ length: 30 }, (_, i) => [i + 1, i + 1]),
    period = 5,
    result = Array.from( {length : ~~(coords.length / period)}
                       , (_,i) => coords[i*period+period-1]
                       );
console.log(result);

JavaScript：一种从数组中提取每第 5 项的更好方法

JavaScript: a better way to extract every 5th item from an array

javascript

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