按数组中的多个属性对对象进行分组，然后将其值相加

Question

按多个属性对数组中的元素进行分组最符合我的问题，因为它确实是按数组中的多个键对对象进行分组的。问题是，这种解决方案不求和属性值，然后删除重复项，而是将所有重复项嵌套在二维数组中。

预期行为

我有一个对象数组，必须按形状和颜色分组。

var arr = [
    {shape: 'square', color: 'red', used: 1, instances: 1},
    {shape: 'square', color: 'red', used: 2, instances: 1},
    {shape: 'circle', color: 'blue', used: 0, instances: 0},
    {shape: 'square', color: 'blue', used: 4, instances: 4},
    {shape: 'circle', color: 'red', used: 1, instances: 1},
    {shape: 'circle', color: 'red', used: 1, instances: 0},
    {shape: 'square', color: 'blue', used: 4, instances: 5},
    {shape: 'square', color: 'red', used: 2, instances: 1}
];

此数组中的对象只有在它们的形状和颜色相同时才被认为是重复的。如果是，我想分别总结它们的使用的和实例值，然后删除重复项。

因此，在这个示例中，结果数组可能只包含四种组合：方红色，方蓝色，圆红色，圆蓝色

问题

我在这里尝试了一种更简单的方法：

var arr = [
    {shape: 'square', color: 'red', used: 1, instances: 1},
    {shape: 'square', color: 'red', used: 2, instances: 1},
    {shape: 'circle', color: 'blue', used: 0, instances: 0},
    {shape: 'square', color: 'blue', used: 4, instances: 4},
    {shape: 'circle', color: 'red', used: 1, instances: 1},
    {shape: 'circle', color: 'red', used: 1, instances: 0},
    {shape: 'square', color: 'red', used: 4, instances: 4},
    {shape: 'square', color: 'red', used: 2, instances: 2}
];

result = [];

arr.forEach(function (a) {
    if ( !this[a.color] && !this[a.shape] ) {
        this[a.color] = { color: a.color, shape: a.shape, used: 0, instances: 0 };
        result.push(this[a.color]);
    } 
    this[a.color].used += a.used;
    this[a.color].instances += a.instances;
}, Object.create(null));

console.log(result);

但它输出

[{shape: "square", color: "red", used: 11, instances: 9},
{shape: "circle", color: "blue", used: 4, instances: 4}]

而不是预期的结果：

[{shape: "square", color: "red", used: 5, instances: 3},
{shape: "circle", color: "red", used: 2, instances: 1},
{shape: "square", color: "blue", used: 11, instances: 9},
{shape: "circle", color: "blue", used: 0, instances: 0}]

如何让我的函数按形状和颜色正确地对对象进行分组？即总结它们的值并删除重复项？

Answer 1

可以使用哈希表和键对相同的组进行分组。

var array = [{ shape: 'square', color: 'red', used: 1, instances: 1 }, { shape: 'square', color: 'red', used: 2, instances: 1 }, { shape: 'circle', color: 'blue', used: 0, instances: 0 }, { shape: 'square', color: 'blue', used: 4, instances: 4 }, { shape: 'circle', color: 'red', used: 1, instances: 1 }, { shape: 'circle', color: 'red', used: 1, instances: 0 }, { shape: 'square', color: 'blue', used: 4, instances: 5 }, { shape: 'square', color: 'red', used: 2, instances: 1 }],
    hash = Object.create(null),
    grouped = [];
    
array.forEach(function (o) {
    var key = ['shape', 'color'].map(function (k) { return o[k]; }).join('|');
    
    if (!hash[key]) {
        hash[key] = { shape: o.shape, color: o.color, used: 0, instances: 0 };
        grouped.push(hash[key]);
    }
    ['used', 'instances'].forEach(function (k) { hash[key][k] += o[k]; });
});

console.log(grouped);

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Answer 2

使用此方法可以指定多个属性：

 public static groupBy(array, f) {
       let groups = {};
       array.forEach(function (o) {
         var group = JSON.stringify(f(o));
         groups[group] = groups[group] || [];
         groups[group].push(o);
       });
    return Object.keys(groups).map(function (group) {
      return groups[group];
    })
 }

将此方法称为：

var result = Utils.groupBy(arr, function (item) {
            return [item.shape, item.color];
          });

Answer 3

将Array#reduce与辅助对象一起使用，将相似的对象分组。对于每个对象，检查辅助对象中是否存在组合的形状和颜色。如果没有，请使用Object#assign添加到辅助对象，以创建对象的副本，并推送到数组。如果有，则将其值添加到已用和实例。

js lang-js prettyprint-override">var arr = [{"shape":"square","color":"red","used":1,"instances":1},{"shape":"square","color":"red","used":2,"instances":1},{"shape":"circle","color":"blue","used":0,"instances":0},{"shape":"square","color":"blue","used":4,"instances":4},{"shape":"circle","color":"red","used":1,"instances":1},{"shape":"circle","color":"red","used":1,"instances":0},{"shape":"square","color":"blue","used":4,"instances":5},{"shape":"square","color":"red","used":2,"instances":1}];

var helper = {};
var result = arr.reduce(function(r, o) {
  var key = o.shape + '-' + o.color;
  
  if(!helper[key]) {
    helper[key] = Object.assign({}, o); // create a copy of o
    r.push(helper[key]);
  } else {
    helper[key].used += o.used;
    helper[key].instances += o.instances;
  }

  return r;
}, []);

console.log(result);