Check out the full version of Towards Scalable Dataframe Systems from VLDB 2020 [0]. They propose an algebra for dataframes and section 4.4's example succinctly

Check out the full version of Towards Scalable Dataframe Systems from VLDB 2020 [0]. They propose an algebra for dataframes and section 4.4's example succinctly describes the pivot operator. [0] https://arxiv.org/abs/2001.00888 https://arxiv.org/abs/2001.00888