Page 84 is where it shows that maps are a sequence of pairs.
The destructuring in James's code is on vectors -- the pairs in the
sequence.
Hope that helps?
Sean
On Fri, Jun 5, 2015 at 8:11 PM, gvim <gvi...@gmail.com> wrote:
> Yes, I'm fine with the concept. Just can't remember coming across it in
> the textbooks but maybe I wasn't paying attention :)
>
> gvim
>
>
>
> On 06/06/2015 04:08, Sean Corfield wrote:
>
>> 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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--
Sean A Corfield -- (904) 302-SEAN
An Architect's View -- http://corfield.org/
World Singles, LLC. -- http://worldsingles.com/
"Perfection is the enemy of the good."
-- Gustave Flaubert, French realist novelist (1821-1880)
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