Most Efficient Method to GroupBy on an Array of Objects

Javascript Arrays Object Group By Underscore.js

When working with arrays of objects in JavaScript, there may be a need to group the objects based on certain properties and perform calculations on the grouped data. This can be achieved using various methods and libraries. In this article, we will explore the most efficient way to achieve this using the groupBy function from Underscore.js library.

Problem Description

The problem described is to group objects in an array by specific properties and calculate the sum of values within each group. The desired output should resemble the SQL "GROUP BY" method, where the values are merged and not split up.

Here is an example array of objects:

            
                const data = [ 
                    { 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" }
                ];

The GroupBy Function from Underscore.js

Underscore.js is a JavaScript library that provides a wide range of functional programming utilities, including the groupBy function. The groupBy function groups the elements of an array based on a specified criterion and returns an object with the grouped elements.

Implementing GroupBy with Sum Calculation

To achieve the desired output, we can use the groupBy function from Underscore.js and then loop through the resulting object to calculate the sum of values for each group.

            
                const groupedData = _.groupBy(data, 'Phase');
                const summedData = [];

                for (const key in groupedData) {
                    const sum = groupedData[key].reduce((acc, obj) => acc + parseInt(obj.Value), 0);
                    summedData.push({ Phase: key, Value: sum });
                }

                console.log(summedData);

Output

If we group the data by the "Phase" property, the output will be:

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

If we group the data by the "Phase" and "Step" properties, the output will be:

            
                [
                    { 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 }
                ]

Conclusion

The groupBy function from Underscore.js is a powerful tool for grouping objects in an array based on specific properties. By using this function along with a loop to calculate the sums, we can efficiently group and aggregate data in JavaScript.

Feel free to explore more functionalities offered by Underscore.js and experiment with different scenarios to further enhance your data manipulation capabilities.

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