think\Collection::column PHP Method

    public function column($column_key, $index_key = null)
    {
        if (function_exists('array_column')) {
            return array_column($this->items, $column_key, $index_key);
        }
        $result = [];
        foreach ($this->items as $row) {
            $key = $value = null;
            $keySet = $valueSet = false;
            if (null !== $index_key && array_key_exists($index_key, $row)) {
                $keySet = true;
                $key = (string) $row[$index_key];
            }
            if (null === $column_key) {
                $valueSet = true;
                $value = $row;
            } elseif (is_array($row) && array_key_exists($column_key, $row)) {
                $valueSet = true;
                $value = $row[$column_key];
            }
            if ($valueSet) {
                if ($keySet) {
                    $result[$key] = $value;
                } else {
                    $result[] = $value;
                }
            }
        }
        return $result;
    }