code: public function column($columnKey, $indexKey = null)
      {
          return $this->createFrom(Arr::column($this->items, $columnKey, $indexKey));
      }
docs: Returns a bag with the values from a single column, identified by the `$columnKey`.
  
  Optionally, an `$indexKey` may be provided to index the values in the
  returned Bag by the values from the `$indexKey` column.
  
  Example:
  
  $bag = Bag::from([
  ['id' => 10, 'name' => 'Alice'],
  ['id' => 20, 'name' => 'Bob'],
  ['id' => 30, 'name' => 'Carson'],
  ]);
  
  $bag->column('name');
  // => Bag of ['Alice', 'Bob', 'Carson']
  
  $bag->column('name', 'id');
  // => Bag of [10 => 'Alice', 20 => 'Bob', 30 => 'Carson']
  
  @param string|int|null $columnKey The key of the values to return or `null` for no change
  @param string|int|null $indexKey  The key of the keys to return or `null` for no change
  
  @return static