JavaScript中的两个数组内部联接 [英] Two arrays inner join in JavaScript

问题描述

以下是我拥有的2个数组，

Following are the 2 arrays I have,

 var g= [ 
        { id: 36, name: 'AAA', goal: 'yes' },
        { id: 40, name: 'BBB', goal: 'yes' },
        { id: 39, name: 'JJJ', goal: 'yes' },
        { id: 27, name: 'CCC', goal: 'yes' }];

    var c= [ 
        { id: 36, color:"purple" },
        { id: 40, color:"purple" },
        { id: 100, color:"pink"} ];

所需的输出("id"上的左连接):

Desired output(left join on 'id'):

    res = [{ id: 36, name: 'AAA', goal: 'yes' , color:"purple"}, { id: 40, name: 'BBB', goal: 'yes', color:"purple" }]

这是进行合并的现有逻辑，但我正在寻找左连接的逻辑:

here's an existing logic which does merger but I'm looking for a logic for left join:

    function mergeBy(key, data) {
      return Array.from(data
          .reduce((m, o) => m.set(o[key], { ...m.get(o[key]), ...o }), new Map)
          .values()
      );
    }

推荐答案

为您准备了一些加入，请选择！

Here are some joins for you, take your pick!

function* innerJoin(a, b, key) {
    let idx = new Map(b.map(x => [key(x), x]));
    for (let x of a) {
        let k = key(x);
        if (idx.has(k))
            yield {...x, ...idx.get(k)};
    }
}

function* leftJoin(a, b, key) {
    let idx = new Map(b.map(x => [key(x), x]));
    for (let x of a) {
        let k = key(x);
        yield idx.has(k) ? {...x, ...idx.get(k)} : x;
    }
}

function* rightJoin(a, b, key) {
    let idx = new Map(a.map(x => [key(x), x]));
    for (let x of b) {
        let k = key(x);
        yield idx.has(k) ? {...idx.get(k), ...x} : x;
    }
}


//

var A = [
    {id: 1, a: 'a1'},
    {id: 2, a: 'a2'},
    {id: 7, a: 'a3'},
    {id: 8, a: 'a4'}
];

var B = [
    {id: 1, b: 'b1'},
    {id: 2, b: 'b2'},
    {id: 9, b: 'b3'}
];


console.log('INNER:')
console.log(...innerJoin(A, B, x => x.id))
console.log('LEFT')
console.log(...leftJoin(A, B, x => x.id))
console.log('RIGHT')
console.log(...rightJoin(A, B, x => x.id))

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