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From: Terry Reedy on 16 May 2010 15:22
On 5/16/2010 1:36 PM, Thomas wrote:
> Greetings
>
> I am having a darn awful time trying to update a matrix:
>
> row = dict([(x,0) for x in range(3)])
> matrix = dict([(x,row) for x in range(-3,4,1)])
>
> matrix[2][1] += 1
> matrix[-1][2] += 1

Dicts are fine for sparse matrixes, but when filled in, a list of lists
is perhaps easier and more efficient. And you can iterate and be
guaranteed to get the sublists in the expected order.

From: Gregory Ewing on 17 May 2010 03:39
> On 5/16/2010 1:36 PM, Thomas wrote:
>> row = dict([(x,0) for x in range(3)])
>> matrix = dict([(x,row) for x in range(-3,4,1)])
>>
>> matrix[2][1] += 1
>> matrix[-1][2] += 1

Another possibility is to use a single dict with
tuples for the indexes.

matrix = dict([((x, y), 0) for x in range(-3, 4) for y in range(3)])

matrix[2, 1] += 1
matrix[-1, 2] += 1

--
Greg
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