I have a collection of transducers that I use in such cases:
(require '[net.cgrand.xforms :as x]
'[clojure.string :as str])
(into {} (x/by-key (comp (map str/upper-case) (x/into [])))
;=> [[:a "foo"] [:b "bar"] [:a "baz"]])
On Fri, Aug 12, 2016 at 7:14 PM, Moe Aboulkheir <m...@nervous.io> wrote:
> As far as already existing, (grouped-map first (comp str/upper-case
> second) ...) or similar, with https://github.com/plumatic/
> plumbing/blob/master/src/plumbing/core.cljx#L164
>
> Take care,
> Moe
>
> On Fri, Aug 12, 2016 at 6:10 PM, Erik Assum <e...@assum.net> wrote:
>
>> I’ve been working on a new project in java 8 at a new client where I’ve
>> been able to play with streams.
>> In doing so I’ve come across Collectors.groupingBy which has some
>> additional features that group-by doesn’t seem to have.
>>
>> Example:
>> Given
>> (def foos [[:a "foo"] [:b "bar"] [:a "baz"]])
>>
>> (group-by first foos)
>> ;=> {:a [[:a "foo"] [:a "baz"]], :b [[:b "bar"]]}
>>
>> but I’d like the result to be
>> ;=> {:a ["FOO" "BAZ"] :b ["BAR”]}
>>
>> This is solved in javas stream api by something like this:
>>
>> List<List<String>> = [["a", "foo"], ["b" "bar"], ["a", "baz"]];
>>
>> foos
>> .stream()
>> .collect(Collectors.groupingBy(e -> e.get(0),
>> Collectors.mapping(e -> e.get(1).toUpperCase(),
>> Collectors.toList())));
>>
>> Where the key point is that Collectors.groupingBy accepts a mapping
>> function in which to map the values being grouped.
>>
>> So how would one go about writing this in Clojure? I could of-course
>> write something that mapped over the grouped map,
>> but I’d really like to write something like
>>
>> (defn mapping-group-by grouping-fn mapping-fn coll)
>>
>> but I have a suspicion that this already exists in some form already?
>>
>> Erik.
>>
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