Thank you! I had forgotten that discussion at the beginning of July .
Googling the list  also shows mention of PythonQL , which may point to use cases that can guide a Vectorization idea.
 groupby discussion - https://mail.python.org/pipermail/python-ideas/2018-July/051786.html
 google search - https://www.google.ca/search?q=group+by+site%3Ahttps%3A%2F%2Fmail.python.org...
 PythonQL - https://github.com/pythonql/pythonql
On 2019-02-11 10:43, Christopher Barker wrote:
Do take a look in the fairly recent archives of this list for a big discussion of groupby -- it kind of petered out but there were a couple options on the table.