javascript - lodash - 基于多个属性创建唯一列表

Question

我的收藏看起来像这样。

  var list = [{id:'12345', sequence:null}, {id:'12346', sequence:null}, {id:'12347', sequence:null}, {id:'12348', sequence:1}, {id:'12348', sequence:2}, {id:'12349', sequence:1}, {id:'12349', sequence:1}];

我正在尝试获取一个唯一列表，以便具有相同 ID 和序列的对象将只返回其中一个对象(我们这里有 2 个 - {id:'12349', sequence:1})

我的代码

  var uniqueList = _.uniq(list, function(obj) {
    return obj.id && obj.sequence;
  });

我们可以像这样使用 lodash uniq 吗？解决此问题的方法是什么？

Answer 1

您可以使用 uniqBy()计算生成列表的标准，其中 iteratee 回调返回集合中每个项目的 id 和 sequence 的联合值。当您只想将特定属性作为唯一性标准时，尤其是当您集合中的每个对象可能不仅具有 id 和 sequence 属性时，下面的解决方案非常有效。

var result = _.uniqBy(list, v => [v.id, v.sequence].join());

var list = [{
  id: '12345',
  sequence: null
}, {
  id: '12346',
  sequence: null
}, {
  id: '12347',
  sequence: null
}, {
  id: '12348',
  sequence: 1
}, {
  id: '12348',
  sequence: 2
}, {
  id: '12349',
  sequence: 1
}, {
  id: '12349',
  sequence: 1
}, {
  id: '123490',
  sequence: 1,
  extra: 1
}, {
  id: '123490',
  sequence: 1,
  extra: 2
}];

var result = _(list)
  .uniqBy(v => [v.id, v.sequence].join())
  .value();

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.12.0/lodash.js"></script>

或者，如果您的属性包含要用作标准的非原始值(对象或数组)，那么您仍然可以使用上述解决方案，但要加入值数组，您必须使用 JSON.stringify()

var result = _.uniqBy(list, v => JSON.stringify([v.id, v.sequence]));

var list = [{
  id: '12345',
  sequence: null
}, {
  id: '12346',
  sequence: null
}, {
  id: '12347',
  sequence: null
}, {
  id: '12348',
  sequence: 1
}, {
  id: '12348',
  sequence: 2
}, {
  id: '12349',
  sequence: 1
}, {
  id: '12349',
  sequence: 1
}, {
  id: '123490',
  sequence: 1,
  extra: 1
}, {
  id: '123490',
  sequence: 1,
  extra: 2
}];

var result = _.uniqBy(list, v => JSON.stringify([v.id, v.sequence]));

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.12.0/lodash.js"></script>

更新:

对于 lodash3 解决方案，对于具有原始值的属性，您仍然可以使用第一个解决方案中的模式使用 uniq() .

var result = _.uniq(list, v => [v.id, v.sequence].join());

var list = [{
  id: '12345',
  sequence: null
}, {
  id: '12346',
  sequence: null
}, {
  id: '12347',
  sequence: null
}, {
  id: '12348',
  sequence: 1
}, {
  id: '12348',
  sequence: 2
}, {
  id: '12349',
  sequence: 1
}, {
  id: '12349',
  sequence: 1
}, {
  id: '123490',
  sequence: 1,
  extra: 1
}, {
  id: '123490',
  sequence: 1,
  extra: 2
}];

var result = _.uniq(list, v => [v.id, v.sequence].join());

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.1/lodash.js"></script>

对于非原始属性，您仍然可以将上面的第二个示例与 uniq() 一起使用

var result = _.uniq(list, v => JSON.stringify([v.id, v.sequence]));

var list = [{
  id: '12345',
  sequence: null
}, {
  id: '12346',
  sequence: null
}, {
  id: '12347',
  sequence: null
}, {
  id: '12348',
  sequence: 1
}, {
  id: '12348',
  sequence: 2
}, {
  id: '12349',
  sequence: 1
}, {
  id: '12349',
  sequence: 1
}, {
  id: '123490',
  sequence: 1,
  extra: 1
}, {
  id: '123490',
  sequence: 1,
  extra: 2
}];

var result = _.uniq(list, v => JSON.stringify([v.id, v.sequence]));

document.write('<pre>' + JSON.stringify(result, 0, 4) + '</pre>');

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.1/lodash.js"></script>