Itβs because if you treat a hash map as a sequence β as `for` does β you get a
sequence of pairs (key/value β map entries):
(seq {:a 1 :b 2})
;;=> ([:a 1] [:b 2])
Does that help?
Sean
> On Jun 5, 2015, at 7:41 PM, gvim <gvi...@gmail.com> wrote:
>
> I must re-read "Clojure Programming" (O'Reilly) in that case as I don't
> recall the authors mentioning this kind of destructuring.
>
> gvim
>
>
> On 06/06/2015 03:33, Fluid Dynamics wrote:
>> On Friday, June 5, 2015 at 10:07:05 PM UTC-4, g vim wrote:
>>
>> That works but I missed this possibility because I'm still not clear
>> how:
>>
>> (group-by :email signs)
>>
>> .... which produces a map of the form:
>>
>> {"a...@gmail.com <javascript:>"
>> [{:email "a...@gmail.com <javascript:>", :sign "Cancer",
>> :planet "Mars", :surname
>> "Blogs", :first_name "Joe"}
>> ..... ]}
>>
>> .... can be destructured with the vector [email signs]. I assumed a map
>> must be destructured with a map but couldn't find a solution as the map
>> keys are unique values, ie. email addresses.
>>
>>
>> The code was (for [[email signs] (group-by...)]...). The for iterates
>> over the map produced by group-by, producing individual map entries, and
>> map entries can be treated as two-element seqs/vectors of [key value],
>> which is what the destructuring does here, putting the key in local
>> binding email and the value, a vector with maps in it, in signs.
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