按值合并数组中的对象并获取每个对象的计数

Question

给定以下对象数组:

myArray = [
  {
    item: 'Item 1',
    material: 'Material1',
    type: 'head'
  },
  {
    item: 'Item 1',
    material: 'Material1',
    type: 'head'
  },
  {
    item: 'Item 2',
    material: 'Material2',
    type: 'shell'
  },
  {
    item: 'Item 1',
    material: 'Material1',
    type: 'head'
  },
  {
    item: 'Item 2',
    material: 'Material2',
    type: 'shell'
  },
  {
    item: 'Item 3',
    material: 'Material3',
    type: 'support'
  },
  {
    item: 'Item 1',
    material: 'Material1',
    type: 'head'
  },
  {
    item: 'Item 3',
    material: 'Material3',
    type: 'support'
  },
  {
    item: 'Item 2',
    material: 'Material2',
    type: 'shell'
  }
]

我需要将这些item值与count 组合在一起,以便得到一个如下所示的数组:

var myResultArray = [
  {
    item: 'Item 1',
    material: 'Material1',
    type: 'head'
    count: 4
  },
  {
    item: 'Item 2',
    material: 'Material2',
    type: 'shell'
    count: 3
  },
  {
    item: 'Item 3',
    material: 'Material3',
    type: 'support'
    count: 2
  },
]

最简单的方法是什么？我偏爱Lodash,但我对其他选择持开放态度.随着_.groupBy()我可以搞定一切与该项目作为重点对象组合在一起:

var myGrouped = _.groupBy(myArray, 'item');

但那只能让我分道扬.. 在这里搜索我看到了很多用途_.reduce()(或者只是简单的.reduce())或者_.map(),但是在这种情况下我无法理解如何使用它们.如果我尝试使用_.groupBy()链接的使用_.map(),像这样

var myGrouped = _(myArray).groupBy('item').map(function(item) {
                  // do stuff here
                });

执行甚至没有到我的地图功能,所以我不确定我做错了什么.

谢谢.

Answer 1

_.groupBy链接_.map是最简单的解决方案.一个适当的回调函数_.map将是:

function (items) {
  items[0].count = items.length;
  return items[0];
}

或者你可以使用ES6箭头功能进一步浓缩它.

const myArray = [{"item":"Item 1","material":"Material1","type":"head"},{"item":"Item 1","material":"Material1","type":"head"},{"item":"Item 2","material":"Material2","type":"shell"},{"item":"Item 1","material":"Material1","type":"head"},{"item":"Item 2","material":"Material2","type":"shell"},{"item":"Item 3","material":"Material3","type":"support"},{"item":"Item 1","material":"Material1","type":"head"},{"item":"Item 3","material":"Material3","type":"support"},{"item":"Item 2","material":"Material2","type":"shell"}];

const myResultArray =
  _(myArray)
    .groupBy('item')
    .map(items => (items[0].count = items.length, items[0]))
    .value();

console.log(myResultArray);

<script src="https://cdn.jsdelivr.net/lodash/4.13.1/lodash.min.js"></script>