如何在 JavaScript 中使用两个对象数组执行内部联接? [英] How can I perform an inner join with two object arrays in JavaScript?

问题描述

我有两个对象数组:

var a = [
  {id: 4, name: 'Greg'},
  {id: 1, name: 'David'},
  {id: 2, name: 'John'},
  {id: 3, name: 'Matt'},
]

var b = [
  {id: 5, name: 'Mathew', position: '1'},
  {id: 6, name: 'Gracia', position: '2'},
  {id: 2, name: 'John', position: '2'},
  {id: 3, name: 'Matt', position: '2'},
]

我想对这两个数组 a 和 b 进行内连接，并创建第三个这样的数组(如果 position 属性不存在，那么它变为空):

I want to do an inner join for these two arrays a and b, and create a third array like this (if the position property is not present, then it becomes null):

var result = [{
  {id: 4, name: 'Greg', position: null},
  {id: 1, name: 'David', position: null},
  {id: 5, name: 'Mathew', position: '1'},
  {id: 6, name: 'Gracia', position: '2'},
  {id: 2, name: 'John', position: '2'},
  {id: 3, name: 'Matt', position: '2'},
}]

我的方法:

function innerJoinAB(a,b) {
    a.forEach(function(obj, index) {
        // Search through objects in first loop
        b.forEach(function(obj2,i2){
        // Find objects in 2nd loop
        // if obj1 is present in obj2 then push to result.
        });
    });
}

但是时间复杂度是O(N^2).我怎样才能在 O(N) 中做到这一点?我的朋友告诉我，我们可以使用 reducer 和 Object.assign.

But the time complexity is O(N^2). How can I do it in O(N)? My friend told me that we can use reducers and Object.assign.

我无法弄清楚这一点.请帮忙.

I'm not able to figure this out. Please help.

推荐答案

解决方法之一.

const a = [
  {id: 4, name: 'Greg'},
  {id: 1, name: 'David'},
  {id: 2, name: 'John'},
  {id: 3, name: 'Matt'},
];

const b = [
  {id: 5, name: 'Mathew', position: '1'},
  {id: 6, name: 'Gracia', position: '2'},
  {id: 2, name: 'John', position: '2'},
  {id: 3, name: 'Matt', position: '2'},
];

const r = a.filter(({ id: idv }) => b.every(({ id: idc }) => idv !== idc));
const newArr = b.concat(r).map((v) => v.position ? v : { ...v, position: null });

console.log(JSON.stringify(newArr));

.as-console-wrapper { max-height: 100% !important; top: 0; }

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