Sum values in an array of objects by value

Question

var Employees = [
    {
        "id": "382740",
        "PayrollID": "8117817425",
        "EmployeeName": "Bob Jones",
        "StartTime": "15:15:00.0000000",
        "FinishTime": "18:15:00.0000000",
        "BreakTime": "45",
        "TotalTime": 2,
        "Comments": "Test",
        "Rate": "19"
    },
    {
        "id": "439617",
        "PayrollID": "8117817425",
        "EmployeeName": "Peter Pan",
        "StartTime": "16:15:00.0000000",
        "FinishTime": "21:15:00.0000000",
        "BreakTime": "60",
        "TotalTime": 4,
        "Comments": "Test",
        "Rate": "32"
    },
    {
        "id": "201636",
        "PayrollID": "5042289623",
        "EmployeeName": "Bob Jones",
        "StartTime": "09:56:00.0000000",
        "FinishTime": "11:56:00.0000000",
        "BreakTime": "45",
        "TotalTime": 1.25,
        "Comments": "Test Comments",
        "Rate": "19"
    },
    {
        "id": "799653",
        "PayrollID": "5042289623",
        "EmployeeName": "Clarke Kent",
        "StartTime": "16:49:00.0000000",
        "FinishTime": "21:49:00.0000000",
        "BreakTime": "60",
        "TotalTime": 4,
        "Comments": "Test",
        "Rate": "19"
    },
    {
        "id": "951567",
        "PayrollID": "5042289623",
        "EmployeeName": "Bob Jones",
        "StartTime": "01:49:00.0000000",
        "FinishTime": "16:49:00.0000000",
        "BreakTime": "60",
        "TotalTime": 14,
        "Comments": "Test",
        "Rate": "10"
    }
]

I have the above array and I want to sum the TotalTime where the EmployeeName is the same. It should return a new array with like entries combined and the TotalTime added. I've used the below but it only returns two values because of Map. Is there a way I can achieve this while still maintaining all the values in the original array?

const CombinedArray = Array.from(Employees.reduce(
                        (m, {EmployeeName, TotalTime}) => m.set(EmployeeName, (m.get(EmployeeName) || 0) + TotalTime,), new Map
                        ), ([EmployeeName, TotalTime]) => ({EmployeeName, TotalTime}));

What is the desired output structure? Some of the properties in the array are different for the same employee across different objects. Would you want to just pick a random object, or the first, or what? — CertainPerformance
– CertainPerformance, Commented Jun 16, 2021 at 2:14
Apologies on that! I just realised, it's all test data which is why they're different. I want to pick a random object so if it's the first it doesn't matter. — Cameron
– Cameron, Commented Jun 16, 2021 at 2:40

CertainPerformance · Accepted Answer · 2021-06-16 02:44:13Z

In the Map, set the value not to the cumulative total time for the employee so far, but to a whole employee object that contains the total time inside it. Spread the first object found so as not to mutate the input.

var Employees=[{id:"382740",PayrollID:"8117817425",EmployeeName:"Bob Jones",StartTime:"15:15:00.0000000",FinishTime:"18:15:00.0000000",BreakTime:"45",TotalTime:2,Comments:"Test",Rate:"19"},{id:"439617",PayrollID:"8117817425",EmployeeName:"Peter Pan",StartTime:"16:15:00.0000000",FinishTime:"21:15:00.0000000",BreakTime:"60",TotalTime:4,Comments:"Test",Rate:"32"},{id:"201636",PayrollID:"5042289623",EmployeeName:"Bob Jones",StartTime:"09:56:00.0000000",FinishTime:"11:56:00.0000000",BreakTime:"45",TotalTime:1.25,Comments:"Test Comments",Rate:"19"},{id:"799653",PayrollID:"5042289623",EmployeeName:"Clarke Kent",StartTime:"16:49:00.0000000",FinishTime:"21:49:00.0000000",BreakTime:"60",TotalTime:4,Comments:"Test",Rate:"19"},{id:"951567",PayrollID:"5042289623",EmployeeName:"Bob Jones",StartTime:"01:49:00.0000000",FinishTime:"16:49:00.0000000",BreakTime:"60",TotalTime:14,Comments:"Test",Rate:"10"}];

const m = new Map();
for (const emp of Employees) {
  if (!m.has(emp.EmployeeName)) m.set(emp.EmployeeName, { ...emp });
  else m.get(emp.EmployeeName).TotalTime += emp.TotalTime;
}
console.log([...m.values()]);

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