js怎么将一个二维数组转换成对象？

Question

二维数组的格式如下：

[["num1","num2","num3","num4"],["1","2","3","4"],["1","2","3","4"],["1","2","3","4"],["1","2","3","4"]];

要求将使用索引为0的每一项作为key值，
后面对应的位置的字符作为value。

输出的格式为：

{
    num1:["1","1","1","1"],
    num2:["2","2","2","2"],
    num3:["3","3","3","3"],
    num4:["4","4","4","4"]
}

求助，该这么转换啊？

先感谢。

---

Answer 1

这不就是一个二重循环的事儿吗？

var arr = [
    ["num1", "num2", "num3", "num4"],
    ["1", "2", "3", "4"],
    ["1", "2", "3", "4"],
    ["1", "2", "3", "4"],
    ["1", "2", "3", "4"]
];

var keys = arr.shift();

const result = keys.reduce((obj, key, i) => {
    obj[key] = arr.map(a => a[i]);
    return obj;
}, {});

console.log(result);

---

10月16日补充说明：

前提是，大数据中每个小数组的长度是一样的（如果不一样需要做容错处理），然后把这个长度取出来作为大循环的长度。之所以这样做，是因为把结果和源数据都看作矩阵的话，它们之间是个转置的关系。

接下来，大循环只能从 1 开始，而不能从 0 开始，因为第 0 项是 key，后面的各项组合起来才是 value。这就是上面把 keys 单独取出来的原因（按正常逻辑是转置后取，对这个问题来说，转置前取更方便，而后取了之后，后面的部分就可以从 0 开始索引了）

剩下的事情就简单了，用个循环把 value 拼出来就好。

上面的代码采用了 reduce 和 map，整个过程实际是把转置和处理混在一起的。建议你自己思考一下如何按逻辑一步步来处理，不考虑优化整合的问题，用一个二重循环把它实现出来（也就是这段说明提到的思路），然后自己给自己回答个。

Answer 2

var arr = [["num1","num2","num3","num4"],["1","2","3","4"],["1","2","3","4"],["1","2","3","4"],["1","2","3","4"]];
var obj = {};
for(var i = 1; i < arr.length; i++) {
    obj[arr[0][i-1]] = arr[i];
}
console.log(obj);

Answer 3

不改变原数组的做法,可能有跟简单的做法

    const crr=[["num1","num2","num3","num4"],["1","2","3","4"],["1","2","3","4"],["1","2","3","4"],["1","2","3","4"]];
    const drr=crr.reduce((pre,cur,i,arr)=>{
        if(i===4) return pre
        pre[arr[0][i]]=arr.reduce((pre1,cur1,j)=>{
            if(j===0) return pre1
            return pre1.concat(cur1[i])
        },[])
        return pre
    },{})
    console.log(crr,drr)