On Thu, Sep 19, 2019 at 10:32 PM Steven D'Aprano <st...@pearwood.info> wrote: > > On Thu, Sep 19, 2019 at 03:26:27PM +1000, Chris Angelico wrote: > > On Thu, Sep 19, 2019 at 3:08 PM Richard Higginbotham <higgi...@gmail.com> > > wrote: > > > > > > I'm not sure if there is any interest by others but I have frequently > > > come across cases where I would like to compare items in one list in > > > another similar to relational algebra. For example are the file names in > > > A in B and if so return a new list with those items. Long story short, I > > > wrote some functions to do that. They are quite simple and fast (due to > > > timsort in no small part). Even the plain python code is faster than the > > > built in set functions (afaik). I created a github and put the ones I > > > thought the community might like in there. > > > https://github.com/ponderpanda/listex > > > > > > an example would be > > > a = [1,2,3,4,5,6] > > > b = [1,3,7,4] > > > list_intersection(a,b, sorta=True, sortb=True) > > > > > > returns [1,3,4] > > > > Can you elaborate on how this differs from using the built-in set type > > for set operations? eg is this for situations where the values are not > > all hashable? > > Sets are unordered and can contain no duplicates. Lists are ordered and > can contain duplicates, so you might think of them as "ordered > multisets".
With the sorta/sortb API and the algorithmic assumption that the heads of both lists can be checked, I think the value of element order has been lost, so the only significance is the possibility of duplicates. The given use-case of file names doesn't justify this. So I'm curious what the OP's actual use-case was for using lists here. ChrisA _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/M5T6UKZMPWGDX4T37EFBRT2VJ3ETKGIM/ Code of Conduct: http://python.org/psf/codeofconduct/
