goodwin64 / array.prototype.groupby

Array.prototype.groupBy

Desctiption

Add a groupBy method to Array.prototype so that elements in an array could be grouped by the result of evaluating a function on each element.

The method should return an object, in which for each different value returned by the function there is a property whose value is the array of elements that return the same value.

For example:

[1,2,3,2,4,1,5,1,6].groupBy(val => val % 3);

/*
{
  0: [3, 6],
  1: [1, 4, 1, 1],
  2: [2, 2, 5]
}
*/

Hint

If no function is passed, the element itself should be taken.

[1,2,3,2,4,1,5,1,6].groupBy();

/*
{
  1: [1, 1, 1],
  2: [2, 2],
  3: [3],
  4: [4],
  5: [5],
  6: [6]
}
*/

Write your code in src/index.js

Run test locally npm test