[Cs254f11] Confusion over maps

[Lee Spector]

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