[Numpy-discussion] vectorizing histogram-like computation

[Piotr Luszczek]

Perry Greenfield wrote:
> 
> On Jun 20, 2005, at 3:09 PM, Piotr Luszczek wrote:
> 
>> All,
>>
>> I apologize if this is a dupe. I haven't seen it where I looked.
>>
>> There is numarray.numeric.histogram and numarray.mlab.histogram.
>> What they do is this (more or less):
>>
>> for idx in arr:
>>    histogram[idx] += 1
>>
>> What I want to do is:
>>
>> for idx in arr:
>>    result[idx] ^= value
>>
>> Doing:
>>
>> result[arr] ^= value
>>
>> doesn't work. Which is not surprising because:
>>
>> histogram[arr] += 1
>>
>> doesn't work either.
>>
>> My question is whether there is a way to do it (the XOR example)
>> without using a for loop.
>>
>> Thanks,
>>
>> Piotr
> 
> 
> Not that I'm aware of. It suggests that there may be a need to expand on 
> the histogram-like functionality to handle this sort of thing, though I 
> wonder how often it would be used.

Sparse matrix computations use indirection all the time.
And being able to the calculations in C and in-place would be a good
thing. But then again I don't know if many numarray users use
sparse matrices rather than just make the matrix dense and
use LAPACK.