對物件數組進行分組的最佳方法

Question

對數組中的物件進行分組的最有效方法是什麼？

例如，給定這個物件數組：

[ 
    { 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" }
]

我正在表格中顯示此資訊。我想按不同的方法進行分組，但我想對值進行求和。

我使用Underscore.js 來實現其groupby 功能，這很有幫助，但並不能解決全部問題，因為我不希望它們“拆分”而是“合併”，更像是SQL group by 方法。

我正在尋找能夠計算具體值的總和（如果需要的話）。

因此，如果我執行 groupby Phase，我希望收到：

[
    { Phase: "Phase 1", Value: 50 },
    { Phase: "Phase 2", Value: 130 }
]

如果我執行 groupy Phase / Step，我會收到：

[
    { 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 }
]

是否有一個有用的腳本，或者我應該堅持使用 Underscore.js，然後循環遍歷結果物件來自己計算總計？

Answer 1

使用 ES6 Map 物件：

/**
 * @description
 * Takes an Array, and a grouping function,
 * and returns a Map of the array grouped by the grouping function.
 *
 * @param list An array of type V.
 * @param keyGetter A Function that takes the the Array type V as an input, and returns a value of type K.
 *                  K is generally intended to be a property key of V.
 *
 * @returns Map of the array grouped by the grouping function.
 */
//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;
}


// example usage

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]

關於地圖： https://developer.mozilla.org/en-US /docs/Web/JavaScript/Reference/Global_Objects/Map

Answer 2

如果您想避免使用外部函式庫，您可以簡潔地實作 groupBy() 的普通版本，如下所示：

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"]}