Implement countBy(array, iteratee) so it creates an object whose keys are the results of calling iteratee on each element of array. The value of each key is the number of elements that produced that result. Do not modify the original array.

countBy(array, iteratee);

Arguments

1. array (Array): The array to iterate over.
2. iteratee (Function): The function used to produce a key for each element. It is invoked with one argument: (value).

Returns

(Object): Returns the composed aggregate object.

Examples

countBy([6.1, 4.2, 6.3], Math.floor);
// => { '4': 1, '6': 2 }

countBy([{ n: 3 }, { n: 5 }, { n: 3 }], (o) => o.n);
// => { '3': 2, '5': 1 }

countBy([], (o) => o); // => {}

countBy([{ n: 1 }, { n: 2 }], (o) => o.m); // => { undefined: 2 }

Resources

• Lodash _.countBy