[Pyrex] Sparse vectors using dicts in Pyrex.

[Andrew Straw]

You write " the sparse vector implementation in scipy". I just wanted to 
make sure that you are aware that there actually are more than one 
format? (csc, csr, dok, at least)

Daniel Yarlett wrote:
> Hi,
>
> I'm having trouble finding any information on this question, so I hope  
> the solution isn't too obvious.
>
> I have decided to use Python dictionaries to encode sparse vectors  
> that I work with (initial exploration suggested this was faster than  
> using the sparse vector implementation in scipy). If a vector has a  
> non-zero value at a given index, the integer index is used as key to  
> the appropriate value. E.g. if the 7th element of a vector is equal to  
> 3.2 then I would write something like:
>
> vector = {}
> vector[7] = 3.2
>
> This works pretty well, except that I wish to expose the dictionary  
> type using Pyrex so that I can hopefully improve the speed of my  
> implementation. I was wondering if anyone could point me to a simple  
> example in which a Pyrex function receives a dictionary and (a) gets  
> the integer keys (indices) of this dictionary, and (b) does something  
> simple like computes the sum of the vector (where each value is cast  
> as a double, say). As I said, I haven't been able to find any  
> documentation on this, and my knowledge of the C API for Python is too  
> underdeveloped to allow me to figure this out on my own.
>
> Also, does anyone have any thoughts on the potential speed benefits of  
> using Pyrex in this instance as opposed to using Python's built-in  
> dictionary methods?
>
> Many thanks,
>
> Dan.
>
>
>
>
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