On Thu, Jun 28, 2018 at 4:34 PM Chris Barker via Python-ideas < [email protected]> wrote:
> On Thu, Jun 28, 2018 at 4:23 PM, Greg Ewing <[email protected]> > wrote: > >> Nicolas Rolin wrote: >> >>> student_by_school = {group_by(school): student for school, student >>> in student_school_list} >>> >> >> In the spirit of making the target expression look like >> a template for the generated elements, >> >> {school: [student...] for school, student in student_school_list} > > > hmm -- this seems a bit non-general -- would this only work for a list? > maybe you would want a set, or??? > > so could be get a defaultdict comprehension with something like: > > { school: (default_factory=list, student) for school, student in > student_school_list } > > But I can't think of an reasonable syntax to make that work. > Many languages with a group-by or grouping function choose to return a mapping of sequences, requiring any reduction, aggregation, or transformation of those sequences to be performed after the grouping.
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