Javascript:取数组的每个第 n 个元素 [英] Javascript: take every nth Element of Array

问题描述

我得到一个数据数量未知的数组.但我只有预定义的数据量要显示/存储.如何在 JavaScript 中获取初始数组的每个第 n 个元素并减少它?

例如:我得到一个大小为 10000 的数组，但只能显示 n=2k 个元素.

我是这样试的:delta= Math.round(10*n/size)/10 = 0.2 -> 取初始数组的每 5 个元素.

for (i = 0; i 

对于 0.2，它始终为 0，但对于其他一些增量 (0.3)，它可以正常工作.delta=0.4 也一样，我工作，但每隔一个 Element 就会被占用.我该怎么做才能让它发挥作用?

解决方案

也许有一个解决方案:

避免使用过滤器，因为您不想循环超过 10 000 个元素！只需使用 for 循环直接访问它们！

var log = function(val){document.body.innerHTML+='<div></pre>'+val+'</pre></div>'}var oldArr = [0,1,2,3,4,5,6,7,8,9,10]var arr = [];无功maxVal = 5;var delta = Math.floor( oldArr.length/maxVal );//避免过滤，因为你不想要//循环超过 10000 个元素！//只需使用 for 循环直接访问它们！//|//Vfor (i = 0; i < oldArr.length; i=i+delta) {arr.push(oldArr[i]);}log('delta :' + delta + 'length = ' + oldArr.length);日志(arr);

I get an Array with an unknown Number of data. But I only have an predefined amount of data to be shown/store. How can I take every nth Element of the initial Array and reduce it in JavaScript?

Eg.: I get an Array with size=10000, but are only able to show n=2k Elements.

I tried it like that: delta= Math.round(10*n/size)/10 = 0.2 -> take every 5th Element of the initial Array.

for (i = 0; i < oldArr.length; i++) {
  arr[i] = oldArr[i].filter(function (value, index, ar) {
    if (index % delta != 0) return false;
    return true;
  });
}

With 0.2 it´s always 0, but with some other deltas (0.3) it is working. Same for delta=0.4, i works, but every second Element is taken with that. What can I do to get this to work?

解决方案

Maybe one solution :

avoid filter because you don't want to loop over 10 000 elements ! just access them directly with a for loop !

 
var log = function(val){document.body.innerHTML+='<div></pre>'+val+'</pre></div>'} 

var oldArr = [0,1,2,3,4,5,6,7,8,9,10]
var arr = [];

var maxVal = 5;

var delta = Math.floor( oldArr.length / maxVal );

// avoid filter because you don't want
// to loop over 10000 elements !
// just access them directly with a for loop !
//                                 |
//                                 V
for (i = 0; i < oldArr.length; i=i+delta) {
  arr.push(oldArr[i]);
}


log('delta : ' + delta + ' length = ' + oldArr.length) ;
log(arr);

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