Write this accumuator in a functional style
Wolfgang Maier
wolfgang.maier at biologie.uni-freiburg.de
Tue Jul 11 02:47:12 EDT 2017
On 07/11/2017 08:11 AM, Steven D'Aprano wrote:
> I have a colleague who is allergic to mutating data structures. Yeah, I
> know, he needs to just HTFU but I thought I'd humour him.
>
> Suppose I have an iterator that yields named tuples:
>
> Parrot(colour='blue', species='Norwegian', status='tired and shagged out')
>
> and I want to collect them by colour:
>
> accumulator = {'blue': [], 'green': [], 'red': []}
> for parrot in parrots:
> accumulator[parrot.colour].append(parrot)
>
>
> That's pretty compact and understandable, but it require mutating a bunch
> of pre-allocated lists inside an accumulator. Can we re-write this in a
> functional style?
>
> The obvious answer is "put it inside a function, then pretend it works by
> magic" but my colleague's reply to that is "Yes, but I'll know that its
> actually doing mutation inside the function".
>
>
> Help me humour my colleague.
>
>
>
Hmm, isn't this just asking for itertools.groupby on the parrots sorted
by colour?
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