[Numpy-discussion] Fast iteration ...

Hari Sundar hsundar at gmail.com
Tue Aug 23 05:31:12 EDT 2005


I am trying to compute the histogram of an ND image. I have been able to use 
the array operation for a part of it and that makes it quite fast. There is 
one part of my code that I have not been able to vectorize and is therefore 
quite slow. I was wondering if there is a faster way to do this, since this 
is substantially slower than what I would get from C code.

# a and b are arrays (ND)

sz = product(a.shape)
ai = a.flat
bi = b.flat

for i in range(sz):
hist_j[bi[i], ai[i]] += 1
hist_a[ai[i]] += 1
hist_b[bi[i]] += 1


इयं विसृष्टिर्यतऽआबभूव यदि वा दधे यदि वा न । 
योऽअयस्याध्यक्षः परमे व्योमन्त्सोऽअङ्ग वेद यदि वा न वेद ।।

Whence all creation had its origin,
He, whether he fashioned it or whether He did not,
He, who surveys it all from the highest heaven,
He knows - or maybe even He does not know. 

~Rg veda
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