[Cs254f11] Confusion over maps

[Wm. Josiah Erikson]

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=>
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> --
> 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
>