<p>什么是在数组中分组对象的最有效方法？</p> <p>例如，给定以下对象数组：</p> <pre class="brush:php;toolbar:false;">[ { Phase: "Phase 1", Step: "Step 1", Task: "Task 1", Value: "5" }, { Phase: "Phase 1", Step: "Step 1", Task: "Task 2", Value: "10" }, { Phase: "Phase 1", Step: "Step 2", Task: "Task 1", Value: "15" }, { Phase: "Phase 1", Step: "Step 2", Task: "Task 2", Value: "20" }, { Phase: "Phase 2", Step: "Step 1", Task: "Task 1", Value: "25" }, { Phase: "Phase 2", Step: "Step 1", Task: "Task 2", Value: "30" }, { Phase: "Phase 2", Step: "Step 2", Task: "Task 1", Value: "35" }, { Phase: "Phase 2", Step: "Step 2", Task: "Task 2", Value: "40" } ]</pre> <p>我正在一个表格中显示这些信息。我想按不同的方法进行分组，但我想要对值进行求和。</p> <p>我正在使用Underscore.js的groupby函数，它很有帮助，但并不能完全满足需求，因为我不想把它们“分开”，而是“合并”，更像SQL的group by方法。</p> <p>我想要的是能够对特定的值进行求和（如果需要的话）。</p> <p>所以，如果我按<code>Phase</code>进行分组，我想要得到：</p> <pre class="brush:php;toolbar:false;">[ { Phase: "Phase 1", Value: 50 }, { Phase: "Phase 2", Value: 130 } ]</pre> <p>如果我按<code>Phase</code> / <code>Step</code>进行分组，我想要得到：</p> <pre class="brush:php;toolbar:false;">[ { Phase: "Phase 1", Step: "Step 1", Value: 15 }, { Phase: "Phase 1", Step: "Step 2", Value: 35 }, { Phase: "Phase 2", Step: "Step 1", Value: 55 }, { Phase: "Phase 2", Step: "Step 2", Value: 75 } ]</pre> <p>是否有一个有用的脚本可以实现这个功能，或者我应该继续使用Underscore.js，然后通过循环遍历结果对象来进行求和？</p>

/**
 * @description
 * 接受一个类型为V的数组和一个分组函数，返回按照分组函数分组的数组的Map。
 *
 * @param list 类型为V的数组。
 * @param keyGetter 一个函数，接受类型为V的数组作为输入，并返回类型为K的值。
 *                  K通常是V的属性键。
 *
 * @returns 按照分组函数分组的数组的Map。
 */
//export function groupBy(list: Array, keyGetter: (input: V) => K): Map> {
//    const map = new Map>();
function groupBy(list, keyGetter) {
    const map = new Map();
    list.forEach((item) => {
         const key = keyGetter(item);
         const collection = map.get(key);
         if (!collection) {
             map.set(key, [item]);
         } else {
             collection.push(item);
         }
    });
    return map;
}


// 使用示例

const pets = [
    {type:"Dog", name:"Spot"},
    {type:"Cat", name:"Tiger"},
    {type:"Dog", name:"Rover"}, 
    {type:"Cat", name:"Leo"}
];
    
const grouped = groupBy(pets, pet => pet.type);
    
console.log(grouped.get("Dog")); // -> [{type:"Dog", name:"Spot"}, {type:"Dog", name:"Rover"}]
console.log(grouped.get("Cat")); // -> [{type:"Cat", name:"Tiger"}, {type:"Cat", name:"Leo"}]

const odd = Symbol();
const even = Symbol();
const numbers = [1,2,3,4,5,6,7];

const oddEven = groupBy(numbers, x => (x % 2 === 1 ? odd : even));
    
console.log(oddEven.get(odd)); // -> [1,3,5,7]
console.log(oddEven.get(even)); // -> [2,4,6]

var groupBy = function(xs, key) {
  return xs.reduce(function(rv, x) {
    (rv[x[key]] = rv[x[key]] || []).push(x);
    return rv;
  }, {});
};

console.log(groupBy(['one', 'two', 'three'], 'length'));

// => {"3": ["one", "two"], "5": ["three"]}