Add Collection::groupBy
Use array_get to fetch attribute
Added descending sort option to Collection::sortBy()
Removed unused use statements
Merge pull request #3137 from phpmycoder/add_descending_sort_to_collections

Added descending sort option to Collection::sortBy()
code cleanup.
Merge pull request #3117 from Anahkiasen/collection-group

Add Collection::groupBy
added groupBy improvements.