[Tutor] how to understand unhashable type: 'list'

[Christian Witts]

On 2011/11/17 12:26 PM, lina wrote:
> On Thu, Nov 17, 2011 at 6:09 PM, Christian Witts<cwitts at compuscan.co.za>  wrote:
>> On 2011/11/17 11:59 AM, lina wrote:
>>
>> list1
>> [['61', '34', '61', '34'], ['61', '35', '61', '70', '61'], ['61',
>> '70', '61', '34'], ['34', '58', '34', '58']]
>>
>> weight={}
>> weight{list1[0]}=1
>>
>> SyntaxError: invalid syntax
>>
>> weight[list1[0]]=1
>>
>> Traceback (most recent call last):
>>    File "<pyshell#292>", line 1, in<module>
>>      weight[list1[0]]=1
>> TypeError: unhashable type: 'list'
>>
>> I wonder how to count the occurence of the list of lists.
>>
>> Thanks, ^_^
>> _______________________________________________
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>>
>> sum(1 if type(elem) == list else 0 for elem in list1) not work for you if
>> all you want to do is count how many lists you have in your main list ?
> not count how many sublists in the main list.
>
> wanna count the occurence of the sublists,
>
> I mean, something like
>
>>>> dictionary[list1[1]]=occurence
> Traceback (most recent call last):
>    File "<pyshell#298>", line 1, in<module>
>      dictionary[list1[1]]=1
> TypeError: unhashable type: 'list'
>>>>> dictionary[list1[1]]=1
> Traceback (most recent call last):
>    File "<pyshell#298>", line 1, in<module>
>      dictionary[list1[1]]=1
> TypeError: unhashable type: 'list'
>

For that you'll need to convert your list to a hash-able type if you 
want to use dictionaries for your store, easiest would probably to use 
the string representation for it so you could do

 >>> list1 = [['61', '34', '61', '34'], ['61', '35', '61', '70', '61'], 
['61', '70', '61', '34'], ['34', '58', '34', '58']]
 >>> weight = {}
 >>> for elem in list1:
...   if elem.__repr__() in weight:
...       weight[elem.__repr__()] += 1
...   else:
...       weight[elem.__repr__()] = 1
...
 >>> weight
{"['34', '58', '34', '58']": 1, "['61', '70', '61', '34']": 1, "['61', 
'34', '61
', '34']": 1, "['61', '35', '61', '70', '61']": 1}

or

 >>> from collections import defaultdict
 >>> list1 = [['61', '34', '61', '34'], ['61', '35', '61', '70', '61'], 
['61', '7
0', '61', '34'], ['34', '58', '34', '58']]
 >>> weight = defaultdict(int)
 >>> for elem in list1:
...     weight[elem.__repr__()] += 1
...
 >>> weight
defaultdict(<type 'int'>, {"['34', '58', '34', '58']": 1, "['61', '70', 
'61', '34']": 1, "['61', '34', '61', '34']": 1, "['61', '35', '61', 
'70', '61']": 1})

Hope that helps.

-- 

Christian Witts
Python Developer
//
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