如何从js中的对象数组中切片？

Question

我有一个这样的对象数组：

const books =[ 
{id: "1", name: "twilight", category: "Movies", price: 10}, 
{id: "2", name: "jaws", category: "Movies", price: 22}, 
{id: "3", name: "the shining", category: "Movies", price: 1},
{id: "4", name: "beers", category: "Movies", price: 10}, 
{id: "5", name: "apples", category: "Movies", price: 22}, 
{id: "6", name: "mono", category: "Movies", price: 1}
]

尝试分割前 2 个，然后是第二个 2，依此类推。

我怎样才能一次切两本书？

Answer 1

Array.prototype.slice()

slice() 方法将数组的一部分的浅拷贝返回到从开始到结束（不包括结束）选择的新数组对象中。原数组不会被修改。

尝试使用for 循环，每次迭代增加2。将i 的当前值作为start 位置，将i+2 作为end 位置作为方法参数：

const books =[ 
  {id: "1", name: "twilight", category: "Movies", price: 10}, 
  {id: "2", name: "jaws", category: "Movies", price: 22}, 
  {id: "3", name: "the shining", category: "Movies", price: 1},
  {id: "4", name: "beers", category: "Movies", price: 10}, 
  {id: "5", name: "apples", category: "Movies", price: 22}, 
  {id: "6", name: "mono", category: "Movies", price: 1}
]

for(var i=0; i<books.length; i+=2){
  var sliced = books.slice(i, i+2);
  console.log(sliced);
}

Answer 2

您可以使用 slice 函数传递要切片的书籍数量（即 2）：

let slicedBooks = []
for(var i = 0;i < books.length;i+= 2){
    let part_slice = books.slice(i, 2 + i);
    slicedBooks.push(part_slice);
    console.log(part_slice);
}
console.log(slicedBooks);

注意 slice 不会更新 books 数组，而是返回一个新数组。

Answer 3

你可以试试这个切片方法

return books.slice(0,2).map((book, i) => {
      return;
    });

Answer 4

由于您使用的是lodash，因此您可以使用_.chunk (lodash#chunk) 来填充一个数组数组，该数组包含第一个 2，然后是第二个 2，依此类推...

_.chunk(books, 2)

这是一个工作示例：

const books = [ 
    {id: "1", name: "twilight", category: "Movies", price: 10}, 
    {id: "2", name: "jaws", category: "Movies", price: 22}, 
    {id: "3", name: "the shining", category: "Movies", price: 1},
    {id: "4", name: "beers", category: "Movies", price: 10}, 
    {id: "5", name: "apples", category: "Movies", price: 22}, 
    {id: "6", name: "mono", category: "Movies", price: 1}
  ],
  res = _.chunk(books, 2);
  
console.log(res);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>

现在，您有了分块数组，迭代并逐一获取您需要的内容！

Answer 5

使用一个滑动的寡妇迭代器，它一次在一组 2 本书上

function two_at_a_time(arr, func){
    for(var i=0; i < arr.length - 1; i++){
        func(arr[i], arr[i + 1]);
    }
}

two_at_a_time(books, function(current, next){
    console.log(current, next);
});

Answer 6

您可以使用 for 循环，一次 2 步用于索引，并根据当前索引进行切片。

for (var i=0; i<books.length; i+=2) {
    console.log(books.slice(i, i+2));
}

即使有奇数本书，这也有效

Answer 7

你也可以试试这段代码sn-p -

var chunckedArray = function(books, chunkCount){
     var chunks = [];
     while(books.length){
         chunks.push(books.splice(0, chunkCount));
     }
     return chunks;
};

chunckedArray(books, 2); // [Array(2), Array(2), Array(2)]

Answer 8

100% 等于 php

function array_slice (arr, offst, lgth, preserveKeys) { // eslint-disable-line camelcase
  //  discuss at: https://locutus.io/php/array_slice/
  // original by: Brett Zamir (https://brett-zamir.me)
  //    input by: Brett Zamir (https://brett-zamir.me)
  // bugfixed by: Kevin van Zonneveld (https://kvz.io)
  //      note 1: Relies on is_int because !isNaN accepts floats
  //   example 1: array_slice(["a", "b", "c", "d", "e"], 2, -1)
  //   returns 1: [ 'c', 'd' ]
  //   example 2: array_slice(["a", "b", "c", "d", "e"], 2, -1, true)
  //   returns 2: {2: 'c', 3: 'd'}




  var key = ''

  if (Object.prototype.toString.call(arr) !== '[object Array]' || (preserveKeys && offst !== 0)) {
    // Assoc. array as input or if required as output
    var lgt = 0
    var newAssoc = {}
    for (key in arr) {
      lgt += 1
      newAssoc[key] = arr[key]
    }
    arr = newAssoc

    offst = (offst < 0) ? lgt + offst : offst
    lgth = lgth === undefined ? lgt : (lgth < 0) ? lgt + lgth - offst : lgth

    var assoc = {}
    var start = false
    var it = -1
    var arrlgth = 0
    var noPkIdx = 0

    for (key in arr) {
      ++it
      if (arrlgth >= lgth) {
        break
      }
      if (it === offst) {
        start = true
      }
      if (!start) {
        continue
      }++arrlgth
      if (isInt(key) && !preserveKeys) {
        assoc[noPkIdx++] = arr[key]
      } else {
        assoc[key] = arr[key]
      }
    }
    // Make as array-like object (though length will not be dynamic)
    // assoc.length = arrlgth;
    return assoc
  }

  if (lgth === undefined) {
    return arr.slice(offst)
  } else if (lgth >= 0) {
    return arr.slice(offst, offst + lgth)
  } else {
    return arr.slice(offst, lgth)
  }
}