如何在数组的索引0处推送元素[重复]

Posted 2023-03-08

【中文标题】如何在数组的索引0处推送元素[重复]

【英文标题】：how to push an element at index 0 of an array [duplicate]

【发布时间】：2017-05-21 02:29:38

【问题描述】：

我有这样的情况，

我有 2 个array1 作为array1 = ["fruit","vegetables"];

和

array2 = [["apple","banana"],["tomato"]]; // index 0:represent fruit i,e (["apple","banana"]), index 1: vegetables i,e (["tomato"])

我的问题：我怎样才能把push item从array1变成这样我的array2

[["fruit","apple","banana"],["vegetables","tomato"]];

我可以确定index:0 为category。

我的data structure是这两个arrayarray1 = ["fruit","vegetables"];和array2 = [["apple","banana"],["tomato"]];

如果我能得到key value 对array 那对我有好处。

我的样本数据：

array1 = ["fruit","vegetables"];


array2 = [["apple","banana"],["tomato"]]; //expected output :[["fruit","apple","banana"],["vegetables","tomato"]];

【参考方案1】：

使用Array#unshift 方法。

var array1 = ["fruit", "vegetables"],
  array2 = [
    ["apple", "banana"],
    ["tomato"]
  ];

var array3 = array2.map(function(v, i)  // iterate over the array to generate the new array
  var arr = v.slice(); // copy the array
  arr.unshift(array1[i]) // insert element at beginning 
  return arr; /// return generated array
);

console.log(array3)

---

更新：如果您不想创建新数组，则可以避免复制部分。

var array1 = ["fruit", "vegetables"],
  array2 = [
    ["apple", "banana"],
    ["tomato"]
  ];

array2.forEach(function(v, i)  // iterate over the array 
  v.unshift(array1[i]) // insert element at beginning 
);

console.log(array2)

ES6 arrow function：

var array1 = ["fruit", "vegetables"],
  array2 = [
    ["apple", "banana"],
    ["tomato"]
  ];

array2.forEach((v, i) => v.unshift(array1[i]));

console.log(array2)

【参考方案2】：

试试这个Array.map() 和Array.unshift() .unshift() 将数据推入数组[0]index 位置。

array1 = ["fruit","vegetables"];
array2 = [["apple","banana"],["tomato"]]; 

array2.map((a,i) =>  a.unshift(array1[i]))
console.log(array2)