How to Regroup JSON array in JavaScript

Regrouping JSON arrays in JavaScript is crucial for organizing data efficiently, simplifying data management tasks, and ensuring better data integration across systems. Here, we will regroup JSON arrays in JavaScript in two methods to achieve this using the reduce method and an iterative approach.

Using Iterative Method

In this approach, The function begins by initializing an empty object called “group” to store regrouped data. It iterates over each item in the jsonArray using forEach(). Each item’s category property is checked, and if a corresponding key doesn’t exist in the “group” object, one is created with an empty array. Items are then pushed into their respective category arrays. Finally, the function returns the “group” object with regrouped data based on categories.

Example: In this example regrouping JSON array in JavaScript using a loop-based method.

JavaScript

function regroupByCategory(jsonArray) {
    const grouped = {};

    // Iterate over the array
    jsonArray.forEach(item => {
        if (!grouped[item.category]) {
            grouped[item.category] = [];
        }
        
        // Push the item into the array
        grouped[item.category].push(item);
    });

    return grouped;
}

const jsonArray = [
    { id: 1, category: "A" },
    { id: 2, category: "B" },
    { id: 3, category: "A" },
    { id: 4, category: "C" },
    { id: 5, category: "B" },
    { id: 6, category: "A" }
];

const regrouped = regroupByCategory(jsonArray);
console.log(regrouped);

Output

{
  A: [
    { id: 1, category: 'A' },
    { id: 3, category: 'A' },
    { id: 6, category: 'A' }
  ],
  B: [ { id: 2, category: 'B' }, { id: 5, category: 'B' } ],
  C: [ { id: 4, category: 'C' } ]
}

Using Array.reduce()

In this approach, The reduce() method initializes an empty object as the accumulator. It iterates over each item in the jsonArray, grouping them by their category property. If a category key doesn’t exist, it creates one with an empty array. It then pushes items into their respective category arrays. Finally, it returns the grouped object containing the regrouped data.

Example: The below example shows a regrouped JSON array in JavaScript Using Array.reduce().

JavaScript

function regroupByCategory(jsonArray) {
    return jsonArray.reduce((grouped, item) => {
        if (!grouped[item.category]) {
            grouped[item.category] = [];
        }
        grouped[item.category].push(item);
        return grouped;
    }, {});
}
const jsonArray = [
    { id: 1, category: "A" },
    { id: 2, category: "B" },
    { id: 3, category: "A" },
    { id: 4, category: "C" },
    { id: 5, category: "B" },
    { id: 6, category: "A" }
];

const regrouped = regroupByCategory(jsonArray);
console.log(regrouped);

Output

{
  A: [
    { id: 1, category: 'A' },
    { id: 3, category: 'A' },
    { id: 6, category: 'A' }
  ],
  B: [ { id: 2, category: 'B' }, { id: 5, category: 'B' } ],
  C: [ { id: 4, category: 'C' } ]
}