"如何從數組中刪除所有奇數索引（例如：a [1]，a [3] ..）值"

Question

我有一個數組，如var aa = ["a","b","c","d","e","f","g","h","i","j","k","l"]; 我想刪除位於偶數索引上的元素。 所以輸出將是 line aa = ["a","c","e","g","i","k"];

我試過這樣

for (var i = 0; aa.length; i = i++) {
if(i%2 == 0){
    aa.splice(i,0);
}
};

但它不起作用。

Answer 1

使用Array#filter方法

 var aa = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l"]; var res = aa.filter(function(v, i) { // check the index is odd return i % 2 == 0; }); console.log(res);

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如果您想更新現有數組，請執行此操作。

 var aa = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l"], // variable for storing delete count dCount = 0, // store array length len = aa.length; for (var i = 0; i < len; i++) { // check index is odd if (i % 2 == 1) { // remove element based on actual array position // with use of delete count aa.splice(i - dCount, 1); // increment delete count // you combine the 2 lines as `aa.splice(i - dCount++, 1);` dCount++; } } console.log(aa);

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另一種以相反順序（從最后一個元素到第一個元素）迭代 for 循環的方法。

 var aa = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l"]; // iterate from last element to first for (var i = aa.length - 1; i >= 0; i--) { // remove element if index is odd if (i % 2 == 1) aa.splice(i, 1); } console.log(aa);

Answer 2

您可以通過這樣做刪除所有備用索引

或者如果你想存儲在不同的數組中，你可以這樣做。

 var aa = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l"]; var x = []; for (var i = 0; i < aa.length; i = i + 2) { x.push(aa[i]); } console.log(x);<\/code><\/pre>

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Answer 3

您可以使用.filter()

 aa =  aa.filter((value, index) => !(index%2));

Answer 4

您可以使用如下所示的臨時變量。

var a = [1,2,3,4,5,6,7,8,9,334,234,234,234,6545,7,567,8]

var temp = [];
for(var i = 0; i<a.length; i++)
   if(i % 2 == 1)
      temp.push(a[i]);

a = temp;

Answer 5

在 Ecmascript 6 中，

var aa = ["a","b","c","d","e","f","g","h","i","j","k","l"];
var bb = aa.filter((item,index,arr)=>(arr.splice(index,1)));
console.log(bb);

Answer 6

const aa = ["a","b","c","d","e","f","g","h","i","j","k","l"];
let bb = aa.filter((items, idx) => idx % 2 !== 0)

Answer 7

我在這里讀到splice具有 O(N) 時間復雜度。 不要循環使用它！

刪除奇數索引的簡單替代方法：

for (let idx = 0; idx < aa.length; idx += 2)
    aa[idx >> 1] = aa[idx];
aa.length = (aa.length + 1) >> 1;

我使用x >> 1作為Math.floor(x/2)的快捷方式。