Javascript for/in 循环 - 连接来自两个不同对象的项目？

Question

我在下面有这些数据集，我想合并每组中的数据：

    var data = {};
    var datasets = [
        {"_id":"58d6c806d7c80d5d44a35204","particles":{"timestamp":[1490470918708,1490470962915,1490470967186],"Particles":["108","108","109"]}},
        {"_id":"58d6caf62552b75f26f56f91","particles":{"timestamp":[1490471670888,1490473309103],"Particles":["109","100"]}}
    ];

    datasets.forEach(function(dataset, index) {
        for (var key in dataset.particles) {
            data[key] = dataset.particles[key];
        }
    });
    console.log(data);

结果：

{ timestamp: [ 1490471670888, 1490473309103 ],
  Particles: [ '109', '100' ] }

他们没有加入。我追求的结果：

 { timestamp: [ 1490470918708,1490470962915,1490470967186, 1490471670888, 1490473309103 ],
  Particles: [ '108','108','109', '109', '100' ] }

有什么想法吗？

编辑

当涉及非常大数据时，concat或push是否更快？

Answer 1

您必须连接数组，而不仅仅是分配值。

var data = {};
var datasets = [
    {"_id":"58d6c806d7c80d5d44a35204","particles":{"timestamp":[1490470918708,1490470962915,1490470967186],"Particles":["108","108","109"]}},
    {"_id":"58d6caf62552b75f26f56f91","particles":{"timestamp":[1490471670888,1490473309103],"Particles":["109","100"]}}
];

datasets.forEach(function(dataset, index) {
  for (var key in dataset.particles) {

    // Check if key already exists.
    if( data[key] === undefined )
      data[key] = [];

    // Add current timestamps.
    data[key] = data[key].concat(dataset.particles[key]);
  }
});
console.log(data);

Answer 2

希望这是需要的:

var data = {};
var datasets = [{
    "_id": "58d6c806d7c80d5d44a35204",
    "particles": {
      "timestamp": [1490470918708, 1490470962915, 1490470967186],
      "Particles": ["108", "108", "109"]
    }
  },
  {
    "_id": "58d6caf62552b75f26f56f91",
    "particles": {
      "timestamp": [1490471670888, 1490473309103],
      "Particles": ["109", "100"]
    }
  }
];
var output = {

}
datasets.forEach(function(dataset, index) {
  for (var key in dataset.particles) {
    if (typeof output[key] == 'undefined') {
      output[key] = []
    }
    //console.log(dataset.particles[key])
    for (var k of dataset.particles[key]) {
      output[key].push(k)
    }

  }
});
console.log(output);

Answer 3

在 函数式编程 风格中，您可以使用 reduce 和 Object.keys:

var datasets = [
    {"_id":"58d6c806d7c80d5d44a35204","particles":{"timestamp":[1490470918708,1490470962915,1490470967186],"Particles":["108","108","109"]}},
    {"_id":"58d6caf62552b75f26f56f91","particles":{"timestamp":[1490471670888,1490473309103],"Particles":["109","100"]}}
];

var data = datasets.reduce ( (acc, {particles}) =>
    Object.keys(particles).reduce ( (acc, key) =>
        (acc[key] = (acc[key] || []).concat(particles[key]), acc), acc
), {} );
    
console.log(data);

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

替代 push 而不是 concat，以防性能出现问题：

var datasets = [
    {"_id":"58d6c806d7c80d5d44a35204","particles":{"timestamp":[1490470918708,1490470962915,1490470967186],"Particles":["108","108","109"]}},
    {"_id":"58d6caf62552b75f26f56f91","particles":{"timestamp":[1490471670888,1490473309103],"Particles":["109","100"]}}
];

var data = datasets.reduce ( (acc, {particles}) =>
    Object.keys(particles).reduce ( (acc, key) =>
        ((acc[key] = (acc[key] || [])).push(...particles[key]), acc), acc
), {} );
    
console.log(data);

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

但是请注意，在这个版本的代码中，push 将获取 particles[key] 中的每个单独的数组元素作为参数，这些元素占用堆栈 space，而堆栈又是有限的。参见 "Is there a max number of arguments JavaScript functions can accept?"。您可以通过对 particles[key] 中的每个单独元素执行单独的 push 调用来克服此限制，但这会降低性能。所以最后你可以使用 concat 版本更好。

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