[Numpy-discussion] Want to eliminate direct for-loop

eat e.antero.tammi@gmail....
Sat Feb 11 17:12:14 CST 2012


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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