Hierarchical data structures

DataFrame can represent hierarchical data structures using two special types of columns:

• ColumnGroup is a group of columns

• FrameColumn is a column of dataframes

You can read DataFrame from json or from in-memory object graph preserving original tree structure.

Hierarchical columns can also appear as a result of some modification operations:

• group produces ColumnGroup

• groupBy produces FrameColumn

• pivot may produce FrameColumn

• split of FrameColumn will produce several ColumnGroup

• implode converts ColumnGroup into FrameColumn

• explode converts FrameColumn into ColumnGroup

• merge converts ColumnGroup into FrameColumn

• etc.

Operations in the navigation tree are grouped such that you can find operations and their respective inverse together, like group and ungroup. This allows you to quickly find out how to simplify any hierarchical structure you come across.