Oh..I still didn't understand that we can pass a list includes array.. Modified as below.
```
    index : a column, Grouper, array which has the same length as data, or list of them.
        Keys to group by on the pivot table index.
        If an array is passed, it is being used as the same manner as column values.
    columns : a column, Grouper, array which has the same length as data, or list of them.
        Keys to group by on the pivot table column.
        If an array is passed, it is being used as the same manner as column values. 
```