[Numpy-discussion] Fast histogram

Zachary Pincus zachary.pincus@yale....
Thu Apr 17 12:09:13 CDT 2008


>> But even if indices = array, one still needs to do something like:
>> for index in indices: histogram[index] += 1
>>
>> Which is slow in python and fast in C.
>>
>>
> I thought of a broadcasting approach... what are the chances that a  
> simple
>
> bins[:] = 0
> bins[ img.flat ] += 1

That doesn't work cumulatively, it seems. Some bins get a value of  
'1', but it never gets incremented past that.

It was worth a try, though... in some cases in-place updating seems to  
work this way (which is usually a source of confusion on this list,  
not the desired result!)

Zach


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