Function groupBy

groupBy<T, K>(array, getKey): Map<K, T[]>
Groups items by grouping function.
Type Parameters
- T
- K
Parameters
- array: T[]
  The items to group.
- getKey: ((item: T, index: number) => K)
  A function that returns a key indicating which group the item belongs to.
  - - (item, index): K
    - Parameters
      item: T
      index: number
      Returns K
Returns Map<K, T[]>
An object containing groups, keyed by group key. The order of items is preserved within each group.