CODE EXAMPLE FOR JAVASCRIPT

Group an Array By an Object Property, array, object

const groupBy = (arr, groupFn) =>
  arr.reduce(
    (grouped, obj) => ({
      ...grouped,
      [groupFn(obj)]: [...(grouped[groupFn(obj)] || []), obj],
    }),
    {}
  );
const people = [
  { name: 'Matt' },
  { name: 'Sam' },
  { name: 'John' },
  { name: 'Mac' },
];
const groupedByNameLength = groupBy(people, (person) => person.name.length);
/**
{
  '3': [ { name: 'Sam' }, { name: 'Mac' } ],
  '4': [ { name: 'Matt' }, { name: 'John' } ]
}
 */
console.log(groupedByNameLength);