JS中的groupBy方法

最近工作中需要寫一些運營數據報表的頁面，后端返回的數據都是未處理過的json，所以，大量的運算任務交給了前端來做，這其中有一個功能就是對數據進行分組，一開始我自己也嘗試寫了一些，但代碼量比較大，顯得很繁瑣，直到后來在stackoverflow上看到了某位大牛寫的方法，非常簡潔優雅，自己也進行修改簡化。代碼如下：

function groupBy( array , id ) {
    let groups = {};
    array.forEach( function( o ) {
        let group = JSON.stringify( o[id] );
        groups[group] = groups[group] || [];
        groups[group].push( o );
    });
    return Object.values(groups);
}
let name = "name"
let list = [
    {"name": "John","Average":15,"High":10,"DtmStamp":1358226000000},
    {"name": "Jane","Average":16,"High":92,"DtmStamp":1358226000000},
    {"name": "Jane","Average":17,"High":45,"DtmStamp":1358226000000},
    {"name": "John","Average":18,"High":87,"DtmStamp":1358226000000},
    {"name": "Jane","Average":15,"High":10,"DtmStamp":1358226060000},
    {"name": "John","Average":16,"High":87,"DtmStamp":1358226060000},
    {"name": "John","Average":17,"High":45,"DtmStamp":1358226060000},
    {"name": "Jane","Average":18,"High":92,"DtmStamp":1358226060000}
];
let sorted = groupBy(list, name);
console.log(sorted);

1. 函數groupBy有兩個形參，一為對象數組，二為指定分類方式的key；
2. groupBy函數內，先創建一個空對象；
3. 然后forEach遍歷對象數組，遍歷時要執行的函數中只有一個形參o（數組中的每個元素）；
4. 由於下面函數調用是想用name來分組，因此let group = JSON.stringify( f(o) )，相當於先獲取到對象數組list中的name屬性對應的屬性值並放入數組中：["John"]，然后再將屬性值轉換為json字符串：'["John"]'；
5. groups[group] = groups[group] || []，在js中對象也是關聯數組，因此這里相當於做了兩件事，一是把group作為groups的key，二是將對應的value初始化，第一次執行為空數組，循環執行時找到相同的name時保持不變；
6. groups[group].push( o )，這句相當於把list中每個對象壓入數組中作為value；
7. 最后，Object.values(groups)是取出groups對象中的所有values,返回分好了組的二維數組，至此大功告成~~~

[ [ { name: 'John', Average: 15, High: 10, DtmStamp: 1358226000000 },
    { name: 'John', Average: 18, High: 87, DtmStamp: 1358226000000 },
    { name: 'John', Average: 16, High: 87, DtmStamp: 1358226060000 },
    { name: 'John', Average: 17, High: 45, DtmStamp: 1358226060000 } ],
  [ { name: 'Jane', Average: 16, High: 92, DtmStamp: 1358226000000 },
    { name: 'Jane', Average: 17, High: 45, DtmStamp: 1358226000000 },
    { name: 'Jane', Average: 15, High: 10, DtmStamp: 1358226060000 },
    { name: 'Jane', Average: 18, High: 92, DtmStamp: 1358226060000 } ] ]