How can I group an array of objects by a specific property and consolidate other properties into arrays?

Grouping Array Items by Object Property

Given an array of objects with group and color properties, the goal is to group the items by their group values, consolidating the color values for each group.

Problem

The provided array looks like this:

myArray = [
  {group: "one", color: "red"},
  {group: "two", color: "blue"},
  {group: "one", color: "green"},
  {group: "one", color: "black"}
]

The desired output is an array like this:

myArray = [
  {group: "one", color: ["red", "green", "black"]},
  {group: "two", color: ["blue"]}
]

Solution

1. Create a Map of Group Names to Values: Use the reduce() method to create a mapping from group names to arrays of colors.
2. Transform into Desired Format: Create a new array by iterating over the map's keys and creating an object for each group, with its group property set to the key and its color property set to the array of colors associated with that key.

Below is a JavaScript implementation:

var myArray = [
    {group: "one", color: "red"},
    {group: "two", color: "blue"},
    {group: "one", color: "green"},
    {group: "one", color: "black"}
];

var group_to_values = myArray.reduce(function (obj, item) {
    obj[item.group] = obj[item.group] || [];
    obj[item.group].push(item.color);
    return obj;
}, {});

var groups = Object.keys(group_to_values).map(function (key) {
    return {group: key, color: group_to_values[key]};
});

console.log("groups:");
console.log(JSON.stringify(groups, null, 4));

This code creates the desired output, with the items grouped by their group property and their color values consolidated into arrays.

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