Thanks Michal -
I have done a little digging into juxt (reading the great write up
that Sean previously posted here - great post by the way) and it is a
very slick way to deal with this issue. I am always amazed at the
createive and concise solutions that Clojure enables.
Thanks much for all of your help guys.
On Apr 21, 12:36 pm, Michał Marczyk <michal.marc...@gmail.com> wrote:
> On 21 April 2010 19:02, Base <basselh...@gmail.com> wrote:
>
> > I am having a hard time destructuring a nested data structure.
>
> > I am starting out with:
>
> > {:tag :column,
> > :attrs nil,
> > :content
> > [{:tag :name, :attrs nil, :content ["agecat"]}
> > {:tag :value, :attrs nil, :content ["nil"]}
> > {:tag :threshold, :attrs nil, :content ["0.05"]}]}
>
> > and am looking to get:
>
> > {:column "agecat", :value "nil", :threshold "0.05"}
>
> If I understand correctly, you want to take the :tag from the
> top-level map, then reach into the :content vector and extract the
> maps with either :name or :threshold bound to the :tag key and get
> something out of their content, right?
>
> If so, then you probably don't want to use destructuring, because you
> don't want to depend on the order in which the submaps occur in the
> :content of the top-level map.
>
> If you can depend on the ordering, then the following would produce
> your desired result (with your example map previously bound to
> #'test-map):
>
> (let [{tag :tag
> [{[tag-val] :content}
> {[value] :content}
> {t :tag [t-val] :content}]
> :content}
> test-map]
> {tag tag-val :value value t t-val})
>
> This attempts to be somewhat smart in that it figures out that the
> final key to be put in the result map is :threshold based on the :tag
> extracted from the last sub-map. So, with consistent structure, that's
> possible with destructuring -- but it is a bit tedious and fragile.
> Best to reserve it for the simpler cases, where the exact format of
> data is likely to remain fixed. (Actually that last part is a must
> with destructuring.)
>
> All in all, I agree with Sean's opinion that an extractor function
> would be a better fit.
>
> Sincerely,
> Michał
>
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