Javascript:获取数组的第n个元素 [英] Javascript: take every nth Element of Array

问题描述

我得到一个数据数未知的数组. 但是我只有预定义的数据量可以显示/存储. 如何获取初始数组的第n个元素，并在JavaScript中进行精简?

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?

例如:我得到一个大小为10000的数组，但只能显示n = 2k个元素.

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

我这样尝试过: delta = Math.round(10 * n/size)/10 = 0.2->取初始数组的第5个元素.

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;
  });
}

使用0.2时，它始终为0，但是使用其他一些增量(0.3)时，它可以工作.同样适用于delta = 0.4，我可以工作，但是每隔一个元素就被占用.我该怎么做才能使它正常工作?

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?

推荐答案

也许是一种解决方案:

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！

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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