二维数组使用includes无效（cannot read property 'includes' of undefined）

Question

程序的目的是arr[i][1]（也就是字符串）去重，并把去重后的结果插入result内，并返回，我的代码如下：

var arr = [ [ 88, 'Bowling Ball' ],
  [ 2, 'Dirty Sock' ],
  [ 3, 'Hair Pin' ],
  [ 12, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 7, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ],
  [ 7, 'Toothpaste' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ],
  [ 7, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ] ];

var result = [[0,'test']];

arr.forEach(function(e,i){
  
  if(!result[i].includes(e[1])){
    result.push(e);
  }
  
});
  

console.log(result);

可是在调试的时候，系统给我的反馈是：TypeError: Cannot read property 'includes' of undefined

我不是很明白，因为result[i]也应该是一个数组才对啊，怎么会出现这种情况呢？

求大神解答，谢谢。

Answer 1

result[0] 是数组，请问 result[1]是什么？

Answer 2

!result[i].includes(e[1])

大哥，你这result在位置0后边都是undefined了，当然TypeError: Cannot read property 'includes' of undefined

Answer 3

字符串去重来了。。

const arr = [ [ 88, 'Bowling Ball' ],
  [ 2, 'Dirty Sock' ],
  [ 3, 'Hair Pin' ],
  [ 12, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 7, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ],
  [ 7, 'Toothpaste' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ],
  [ 7, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ] ];


let hash={"test":0};
arr.forEach((e)=>{
    if(!hash[e[0]]){
        hash[e[1]]=e[0];
    }
});
let result=[];
for(let key in hash){
    const value=hash[key];
    result.push([value,key]);
}

console.log(result);

-------------------------------分割线----------------------------------
眼睛一花，看成序号去重。。将错就错的代码（序号去重）如下

const arr = [ [ 88, 'Bowling Ball' ],
  [ 2, 'Dirty Sock' ],
  [ 3, 'Hair Pin' ],
  [ 12, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 7, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ],
  [ 7, 'Toothpaste' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ],
  [ 7, 'Toothpaste' ],
  [ 2, 'Hair Pin' ],
  [ 3, 'Half-Eaten Apple' ],
  [ 67, 'Bowling Ball' ] ];


let hash={"0":"test"};
arr.forEach((e)=>{
    if(!hash[e[0]]){
        hash[e[0]]=e[1];
    }
});
let result=[];
for(let key in hash){
    const value=hash[key];
    result.push([key,value]);
}

console.log(result);

Answer 4

开始没看清题意，是对数字和字符串都进行了比较。如果只比较字符串部分，只需要把判断中 && 和之前的部分去掉就可以了。

两个内容相同但对象不是同一个的数组不能用 === 比较判等，所以 includes() 没法判断它们的相等性。可以用 every() 或 some() 来逐个判断

const result = arr
    .reduce((all, t) => {
        if (!all.some(x => t[0] === x[0] && t[1] === x[1])) {
            all.push(t);
        }
        return all;
    }, []);

如果不要求按原顺序，可以先排序再判断，更快一些

const result = arr
    .sort((a, b) => a[0] - b[0])
    .reduce((all, t) => {
        if (!all.length) {
            all.push(t);
        } else {
            const last = all[all.length - 1];
            if (!(last[0] === t[0] && last[1] === t[1])) {
                all.push(t);
            }
        }
        return all;
    }, []);

两段代码的结果：