Implement a function groupBy(array, keyOrFn) that groups elements of an array into an object based on a function or property name.

The function should:

• Accept an array of values.
• Accept a key function or a property name string.
• Return an object where each key corresponds to the result of the function or property, and the value is an array of items that match that key.

Example

groupBy([6.1, 4.2, 6.3], Math.floor);
// { '4': [4.2], '6': [6.1, 6.3] }

groupBy(['one', 'two', 'three'], 'length');
// { '3': ['one', 'two'], '5': ['three'] }