减少键上的对象数组并将值求和成数组 [英] Reduce array of objects on key and sum value into array

问题描述

我有以下对象:

data = [
  { name: 'foo', type: 'fizz', val: 9 },
  { name: 'foo', type: 'buzz', val: 3 },
  { name: 'bar', type: 'fizz', val: 4 },
  { name: 'bar', type: 'buzz', val: 7 },
];

使用过的lodash地图:

And used lodash map:

result = _.map(data, function item, idx){
  return {
    key: item[key],
    values: item.value,
  }
}

这将导致:

[
  { key: foo, val: 9 },
  { key: foo, val: 3 },
  { key: bar, val: 4 },
  { key: bar, val: 7 },
]

但是现在我要返回:

[
  { key: 'foo', val: 12 },
  { key: 'bar', val: 11 },
]

我尝试使用reduce似乎只输出到单个对象，然后可以将其转换回数组，但是我觉得必须有一种优雅的方法来使用lodash将源数据直接转换为所需的数据没有所有中间步骤的结果.

I tried using reduce which seems to only output to a single object, which I could then convert back into an array, but I feel like there must be an elegant way to use lodash to go from my source data straight to my desired result without all of the intermediate steps.

我认为这解决了我的确切问题，但似乎不得不将对象转换为上面概述的所需对象数组，需要做很多工作.

I thought this was addressing my exact problem, but it seems like quite a bit of work just to have to convert the object into the desired array of objects outlined above.

干杯.

推荐答案

有趣的是，由于想要通过键累积值，但是又希望将键作为属性键的值，因此并非一帆风顺.所以有点像逆映射减少:

Interestingly not straight forward, because of wanting to accumulate the value by key, but then wanting the key as a value of the property key. So somewhat like an inverse map reduce:

var result = 
    _.chain(data)
        .reduce(function(memo, obj) {
            if(typeof memo[obj.name] === 'undefined') {
                memo[obj.name] = 0;
            } 
            memo[obj.name] += obj.val;
            return memo;
        }, {})
        .map(function (val, key) {
            return {key: key, val: val};
        })
        .value();

为了简洁起见，在es6中:

For the sake of brevity in es6:

_.chain(data)
    .reduce((memo, obj) => {
        memo[obj.name = obj.val] += obj.val;
        return memo; 
    }, {})
    .map((val, key) => ({key, val}))   
    .value();

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