DBIx::DataModel::Schema::ResultAs::Categorize - tree of categorized lists of rows
my $tree = $source->select(..., -result_as => [categorize => ($key1, $key2)]);
Builds a tree of rows through module List::Categorize, with
$key2, etc. as categorization keys. This is quite similar to the
hashref result kind, except that the categorization keys need not be unique : each leaf of the tree will contain lists of rows matching those categories, while the
hashref result kind only keeps the last row matching the given keys.