[Cs254f11] Confusion over maps

[Wm. Josiah Erikson]

You read my mind (or rather, remembered what I'm doing). Thanks, I do 
indeed find that piece of hackery interesting :)
     -Josiah


On 11/15/11 9:59 PM, Lee Spector wrote:
> Ah -- well there may be tradeoffs either way, but you might find this piece of hackery interesting:
>
> (defn foo [x] (+ x 23))
>
> ((eval (read-string (name :foo))) 100)
>
>   -Lee
>
>
> On Nov 15, 2011, at 9:54 PM, Wm. Josiah Erikson wrote:
>
>> Thanks. I think that if I use keywords then I will have trouble calling things the way I need to, because they are dual-purpose, but perhaps I can get clever and figure out a way to do it.
>> I knew there had to be a simple explanation.
>>     -Josiah
>>
>>
>> On 11/15/11 9:48 PM, Lee Spector wrote:
>>> You don't have to have : in front of keys for maps to work properly, but the nice thing about keywords (symbols that start with :) is that they don't have to be quoted. And you seem to have a quoting issue here.
>>>
>>> The simple fix, if you want to continue using those non-keyword keys, is to change:
>>>
>>>> (get test low_note)
>>> to
>>>
>>> (get test 'low_note)
>>>
>>> What you were doing was asking for the value in test for the key which IS THE VALUE of a var called low_note. In other words, it will evaluate test (to get the map), and low_note (to get whatever was bound to that var), and look up the value in low_note in the map that's in test. That *should* give you an error.... and from the fact that it doesn't, and that it's giving you nil instead, I'm guessing that you've actually def'd low_note somewhere, giving it some value... and that value is what you're looking up in the map, and since it doesn't find that you're getting nil.
>>>
>>> If I recreate your map, which requires that I quote all of the symbols as follows:
>>>
>>> (def test
>>> {'average_velocity 37,
>>> 'number_of_different_real_notes 57,
>>> 'most_common_real_note 64,
>>> 'average_real_note 60,
>>> 'average_note 57,
>>> 'low_note 28,
>>> 'high_note 91,
>>> 'std_dev_mostcom 11})
>>>
>>> then I can do:
>>>
>>> (get test 'low_note)
>>>
>>> to get
>>>
>>> 28
>>>
>>> and
>>>
>>> (find test 'low_note)
>>>
>>> to get
>>>
>>> [low_note 28]
>>>
>>> Alternatively, if you used keywords then you could use :low_note both in the map and in the get and find forms.
>>>
>>>   -Lee
>>>
>>>
>>> On Nov 15, 2011, at 9:08 PM, Wm. Josiah Erikson wrote:
>>>
>>>> I don't understand why my "get" and "find" statements aren't working here. Probably really basic (I don't HAVE to have the useful ":" macro in front of the keys to use a map, do I?)
>>>>
>>>> test
>>>> {average_velocity 37,
>>>> number_of_different_real_notes 57,
>>>> most_common_real_note 64,
>>>> average_real_note 60,
>>>> average_note 57,
>>>> low_note 28,
>>>> high_note 91,
>>>> std_dev_mostcom 11}
>>>>
>>>> critic_evolution.core=>
>>>> (get test low_note)
>>>> nil
>>>>
>>>> critic_evolution.core=>
>>>> (keys test)
>>>> (average_velocity
>>>> number_of_different_real_notes
>>>> most_common_real_note
>>>> average_real_note
>>>> average_note
>>>> low_note
>>>> high_note
>>>> std_dev_mostcom)
>>>>
>>>> critic_evolution.core=>
>>>> (find test low_note)
>>>> nil
>>>>
>>>> critic_evolution.core=>
>>>> test
>>>> {average_velocity 37,
>>>> number_of_different_real_notes 57,
>>>> most_common_real_note 64,
>>>> average_real_note 60,
>>>> average_note 57,
>>>> low_note 28,
>>>> high_note 91,
>>>> std_dev_mostcom 11}
>>>>
>>>> critic_evolution.core=>
>>>> (vals test)
>>>> (37 57 64 60 57 28 91 11)
>>>>
>>>> critic_evolution.core=>
>>>> (map? test)
>>>> true
>>>>
>>>> critic_evolution.core=>
>>>> _______________________________________________
>>>> Cs254f11 mailing list
>>>> Cs254f11 at lists.hampshire.edu
>>>> https://lists.hampshire.edu/mailman/listinfo/cs254f11
>>> --
>>> Lee Spector, Professor of Computer Science
>>> Cognitive Science, Hampshire College
>>> 893 West Street, Amherst, MA 01002-3359
>>> lspector at hampshire.edu, http://hampshire.edu/lspector/
>>> Phone: 413-559-5352, Fax: 413-559-5438
>>>
>> _______________________________________________
>> Cs254f11 mailing list
>> Cs254f11 at lists.hampshire.edu
>> https://lists.hampshire.edu/mailman/listinfo/cs254f11
> --
> Lee Spector, Professor of Computer Science
> Cognitive Science, Hampshire College
> 893 West Street, Amherst, MA 01002-3359
> lspector at hampshire.edu, http://hampshire.edu/lspector/
> Phone: 413-559-5352, Fax: 413-559-5438
>

-- 
Wm. Josiah Erikson
Network Engineer
Hampshire College
Amherst, MA 01002
(413) 559-6091