replyr_split: split a data item by values in a column.
Description
Partitions from by values in grouping column, and returns list. Only advised for a
moderate number of groups and better if grouping column is an index.
This plus lapply and replyr::bind_rows is powerful
enough to implement "The Split-Apply-Combine Strategy for Data Analysis"
https://www.jstatsoft.org/article/view/v040i01