Thanks Marko. I do have couple more q's for you just to ensure I got
everything right:
(comp keyset-b key-fn)
> This results in a function that first applies *key-fn*, then *keyset-b*.
> So it's like #(keyset-b (key-fn %)). Let's call this function *predicate*.
1. What exactly happens when an item is passed to #(keyset-b (key-fn %)) ? Does
keyset-b looks up itself (because collections are functions) for the item
which contains *:id X *and returns true/false?
2. Isn't it more idiomatic to write #((key-fn %) keyset-b) ?
3. Does remove loops list-a internally and applies the predicate to each
item? (if the answer is no my head will definitely explode)
Thanks again for your patience :)
Ryan
On Thursday, March 21, 2013 6:09:42 PM UTC+2, Marko Topolnik wrote:
>
> Personal preference. It causes less mental load because it more obviously
> spells out what you are doing.
>
> On Thursday, March 21, 2013 4:58:08 PM UTC+1, Ryan wrote:
>>
>> Thanks a lot Marko. Much better now :)
>>
>> I also wanted to ask you why did you mention in a previous post that you
>> prefer using *remove *than *filter + complement*. Is there a reason for
>> this or just a personal preference?
>>
>> Ryan
>>
>> On Thursday, March 21, 2013 5:37:33 PM UTC+2, Marko Topolnik wrote:
>>>
>>> First we build a set of all the keys in *list-b*:
>>>
>>> (into #{} (map key-fn list-b))
>>>
>>> Let's call that set *keyset-b. *Then we use *keyset-b* as a function
>>> which returns truthy (non-nil) for any key that is contained in it, and
>>> compose it with our *key-fn*:
>>>
>>> (comp keyset-b key-fn)
>>>
>>> This results in a function that first applies *key-fn*, then *keyset-b*.
>>> So it's like #(keyset-b (key-fn %)). Let's call this function *predicate
>>> *.
>>>
>>> Finally, we use *predicate* to *remove* any member of *list-a* for
>>> which it is truthy:
>>>
>>> (remove predicate list-a)
>>>
>>> -marko
>>>
>>> On Thursday, March 21, 2013 4:14:46 PM UTC+1, Ryan wrote:
>>>
>>>> Marko,
>>>>
>>>> Can you please do me a favor and break down the function you suggested
>>>> me? I understand partially how it works but I am having trouble to fully
>>>> get it.
>>>>
>>>> (remove (comp (into #{} (map key-fn list-b)) key-fn) list-a)
>>>>>
>>>>
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