总结对象的数组，每个唯一对象名称计算平均值 [英] Summarize array of objects and calculate average value for each unique object name

问题描述

我有一个数组，像这样：

I have an array like so:

var array = [
     {
       name: "a",
       value: 1 
     },
     {
       name: "a",
       value: 2 
     },
     {
       name: "a",
       value: 3 
     },
     {
       name: "b",
       value: 0 
     },
     {
       name: "b",
       value: 1 
     }
 ];

和我需要一个这样的数组：

And I need an array like this:

var newarray = [
     {
       name: "a",
       value: 2
     },
     {
       name: "b",
       value: 0.5
     }
 ]

当新的阵列具有每一个独特的名字作为平均值的对象。

Where the new array has each unique name as an object with the average value.

有一个简单的方法来做到这一点？

Is there an easy way to accomplish this?

推荐答案

您会通过数组必须循环，计算每个物体的总和计数。这里有一个快速的实现：

You'll have to loop through the array, computing the sum and counts for each object. Here's a quick implementation:

function average(arr) {
    var sums = {}, counts = {}, results = [], name;
    for (var i = 0; i < arr.length; i++) {
        name = arr[i].name;
        if (!(name in sums)) {
            sums[name] = 0;
            counts[name] = 0;
        }
        sums[name] += arr[i].value;
        counts[name]++;
    }

    for(name in sums) {
        results.push({ name: name, value: sums[name] / counts[name] });
    }
    return results;
}

演示

请注意，这种东西可以，如果你使用像库变得更加容易 Underscore.js ：

Note, this kind of thing can be made much easier if you use a library like Underscore.js:

var averages = _.chain(array)
                .groupBy('name')
                .map(function(g, k) {
                    return { 
                        name: k, 
                        value: _.chain(g)
                                .pluck('value')
                                .reduce(function(x, y) { return x + y })
                                .value() / g.length
                    };
                })
                .value();

演示

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