How to group by array of objects

How to group by array of objects?

Source: StackOverflow.com

Question

What is the most efficient way to group by objects in an array? For example, given this array of objects:

    [ 
        { 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" }
    ]

I'd like to groupby different methods, but I want to sum the values.

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

And if I did groupy Phase / Step, I'd receive:

    [
        { 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 }
    ]

Answer

You can do it with this code:

    var data = [ { Phase: "Phase 1", Step: "Step 1", Task: "Task 1", Value: "5" },
                 { Phase: "Phase 1", Step: "Step 1", Task: "Task 2", Value: "10" }];

    var res = alasql('SELECT Phase, Step, SUM(CAST([Value] AS INT)) AS [Value] \
                      FROM ? GROUP BY Phase, Step',[data]);

Try this example at jsFiddle.

BTW: On large arrays (100000 records and more) AlaSQL faster tham Linq. See test at jsPref.

Comments:

• Here I put Value in square brackets, because VALUE is a keyword in SQL
• I have to use CAST() function to convert string Values to number type.