ajuc wrote:
> On 20 Lis, 01:49, nchubrich <[email protected]> wrote:
>> While we're on the topic, where is something like (subtract [1 2 3 3 4
>> 4 5 6] evens) -> (1 3 3 5)? Doesn't seem to be in seq-utils or API.
>> Seems like there should be a parallel "multiset" library for colls, to
>> clojure.set. (I guess there could be two versions of subtract, one
>> that removes \all, and one that removes only as many as are in the
>> subtracted set.) Maybe I will write this unless there is already some
>> such out there
>
> Did you mean remove? It's in core.
>
> (user=> (remove even? [1 2 3 3 4 5 6])
> (1 3 3 5)
and note that you can use a set as the predicate:
(remove #{2 3 5} [1 2 3 4 5 6 7])
=> (1 4 6 7)
So if you wanted to "subtract" two vectors:
(remove (set [2 3 5]) [1 2 3 4 5 6 7])
=> (1 4 6 7)
Doing it "multiset" style (removing only as many as are in the
subtracted set) might require some more thought though, it might be more
efficient to use a hash map representation for your multiset and then do:
(merge-with - {:a 2, :b 1} {:a 1, :b 1})
=> {:a 0 :b 1}
That doesn't remove "zero" values though, which may or may not be a good
thing depending on exactly how you want to use it.
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