[Numpy-discussion] Want to eliminate direct for-loop
Dinesh B Vadhia
dineshbvadhia@hotmail....
Sat Feb 11 18:04:20 CST 2012
Sorry, I copy and pasted the wrong example r result - it should be as you say:
r = array([ 1, 1, 1, 48, 68, 1, 75, 1, 1, 115, 1, 95, 1, 1, 1, 1, 1, 1, 1, 28, 1, 68, 1, 1, 28])
The reason for looking for an alternative solution is performance as the sizes of r, s and c are very large with the for-loop calculation repeated continuously (with different r, s and c).
From: eat
Sent: Saturday, February 11, 2012 3:12 PM
To: Discussion of Numerical Python
Subject: Re: [Numpy-discussion] Want to eliminate direct for-loop
Hi,
On Sat, Feb 11, 2012 at 10:56 PM, Dinesh B Vadhia <dineshbvadhia@hotmail.com> wrote:
Could the following be written without the direct for-loop?
import numpy
# numpy vector r of any data type and length, eg.
r = numpy.ones(25, dtype='int')
# s is a list of values (of any data type), eg.
s = [47, 27, 67]
# c is a list of (variable length) lists where the sub-list elements are index values of r and len(s) = len(c), eg.
c = [[3, 6, 9], [6, 11, 19, 24], [4, 9, 11, 21 ]]
# for each element in each sub-list c, add corresponding s value to the index value in r, eg.
for i, j in enumerate(c):
r[j] += s[i]
So, we get:
r[[3, 6, 9]] += s[0] = 1 + 47 = 48
r[[6, 11, 19, 24]] += s[1] = 1 + 27 = 28
r[[4, 9, 11, 21]] += s[2] = 1 + 67 = 68
ie. r = array([ 1, 1, 1, 95, 68, 1, 122, 1, 1, 162, 1, 95, 1, 1, 1, 1, 1, 1, 1, 28, 1, 68, 1, 1, 28])
Thank-you!
Could you describe more detailed manner about why you want to get rid of that loop? Performance wise? If so, do you have profiled what's the bottleneck?
Please provide also a more detailed description of your problem, since now your current spec seems to yield:
r= array([ 1, 1, 1, 48, 68, 1, 75, 1, 1, 115, 1, 95, 1,
1, 1, 1, 1, 1, 1, 28, 1, 68, 1, 1, 28])
My 2 cents,
-eat
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