Array.prototype.filter（）的原地替代是什么？ [英] What is the in-place alternative to Array.prototype.filter()

问题描述

我有一个数组，我想从中删除一些元素。我不能使用 Array.prototype.filter（），因为我想修改数组（因为它节省了内存分配，对我来说更重要的是，代码在我的用例中更简单）。是否有可以替代 filter 的替代方法，可以类似于 Array.prototype.forEach（）可以用作 Array.prototype.map（）

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编辑：根据要求提供的最小示例：

  function someCallback（array）{
 //做一些事情
 array.filterInPlace（function（elem）{
 var result = / *一些逻辑* / 
返回结果; 
}）
 //做更多的事情
} 
  

解决方案

是否存在过滤器的替代方案

否，但编写自己的代码并不难。这是一种挤出所有不符合条件的值的方法。

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while（i< a.length）{
const val = a [i];
if（condition（val，i，a））a [j ++] = val;
i ++;
}

a.length = j;
返回a;
}

条件的设计与传递给 Array＃filter 的回调具有相同的签名，即（value，index，array）。为了与 Array＃filter 完全兼容，您还可以接受第四个 thisArg 参数。

使用 forEach

使用 forEach 有一个小优点，它会跳过空插槽。此版本：

• 实现 thisArg


• 如果我们尚未遇到失败的元素，则指定Skipps

< pre-class =snippet-code-js lang-js prettyprint-override> function filterInPlace（a，condition，thisArg）{let j = 0; a.forEach（（e，i）=> {if（condition.call（thisArg，e，i，a））{if（i！== j）a [j] = e; j ++;}}）; a.length = j; return a;} a = [1，3]; document.write（'< br> ['，a，']'）; filterInPlace（a，x => true）; document.write（'< ）; b = [1,3，...，5]; document.write（'< br，'['，b，']'）; filterInPlace（b ，x => x！== 5）; document.write（'<'，'b，'] with 5 removed'）;

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I've got an array that I would like to remove some elements from. I can't use Array.prototype.filter(), because I want to modify the array in place (because it saves a memory allocation and, more important for me, makes the code more simple in my use case). Is there an in-place alternative to filter that I can use, maybe analogously to how Array.prototype.forEach() can be used as an in-place variant to Array.prototype.map()?

Edit: Minimum example upon request:

function someCallback(array) {
  // do some stuff
  array.filterInPlace(function(elem) {
    var result = /* some logic */
    return result;
  })
  // do some more stuff
}

解决方案

Is there an in-place alternative to filter

No, but it's not hard to write your own. Here is an approach which squeezes out all the values which fail a condition.

function filterInPlace(a, condition) {
  let i = 0, j = 0;

  while (i < a.length) {
    const val = a[i];
    if (condition(val, i, a)) a[j++] = val;
    i++;
  }

  a.length = j;
  return a;
}

condition is designed to have the same signature as the callback passed to Array#filter, namely (value, index, array). For complete compatibility with Array#filter, you could also accept a fourth thisArg parameter.

Using forEach

Using forEach has the minor advantage that it will skip empty slots. This version:

• Compacts arrays with empty slots
• Implements thisArg
• Skipps the assignment, if we have not yet encountered a failing element

function filterInPlace(a, condition, thisArg) {
  let j = 0;

  a.forEach((e, i) => { 
    if (condition.call(thisArg, e, i, a)) {
      if (i!==j) a[j] = e; 
      j++;
    }
  });

  a.length = j;
  return a;
}

a = [ 1,, 3 ];
document.write('<br>[',a,']');

filterInPlace(a, x=>true);
document.write('<br>[',a,'] compaction when nothing changed');

b = [ 1,,3,,5 ];
document.write('<br>[',b,']');

filterInPlace(b, x=>x!==5);
document.write('<br>[',b,'] with 5 removed');

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