基于回调函数对对象进行分组[重复]

我有一个对象数组，需要根据给定的回调函数“排序”并放入另一个对象中。例如：

var list = [{id: "102", name: "Alice"},
            {id: "205", name: "Bob", title: "Dr."},
            {id: "592", name: "Clyde", age: 32}];


groupBy(list, function(i) { return i.name.length; });

应该返回：

  {
    "3": [{id: "205", name: "Bob", title: "Dr."}],
    "5": [{id: "102", name: "Alice"},
      {id: "592", name: "Clyde", age: 32}]

这是我到目前为止所拥有的，但我被困住了......

function groupBy(arr, cb) {
let result = {};
arr.forEach(function (obj) {
  var group = [];
  group.push(cb(i))
  result[group].push(obj);
}
  return result;
)}

我会怎么做：

 function groupBy(arr, cb){
   const res = {};
   for(const el of arr){
     const key = cb(el);
     (res[key] || (res[key] = [])).push(el);
   }
   return res;
 }

为什么它不起作用：

 function groupBy(arr, cb) {
  let result = {};
  arr.forEach(function (obj) {
    //That creates one group for each obj?
    var group = [];
   //group should contain the obj, not the key?
   group.push(cb(i))
   // Now you are accessing the result by an array as index??
   // And try to push the object to it which will obvipusly fails as you never set result[group] to an array
   result[group].push(obj);
   }
 return result;
//Typo??
)}