numarray :: multiplying all the elements in 1d array

[Suresh Jeevanandam]

Hi all,
Lets say I have an array:
from numarray import *
a = array([ 6, 7, 8, 9, 10, 11, 12])

I want to multiply out all the elements and get the result.

r = 1.0
for i in a:
r = r*i

Is there any faster, efficient way of doing this.

Thanks,

regards,
Suresh

[Mandus]

Re: numarray :: multiplying all the elements in 1d array

Tue, 20 Dec 2005 19:32:13 +0530 skrev Suresh Jeevanandam:[color=blue]
> Hi all,
> Lets say I have an array:
> from numarray import *
> a = array([ 6, 7, 8, 9, 10, 11, 12])
>
> I want to multiply out all the elements and get the result.
>
> r = 1.0
> for i in a:
> r = r*i
>
> Is there any faster, efficient way of doing this.[/color]

You can use multiply.reduce (a) (multiply is a function imported from
numarray).

With regular python you can also do:

from operator import mul
reduce(mul,a)

This work even when 'a' is a plain python list.


--
Mandus - the only mandus around.

[Robert Kern]

Re: numarray :: multiplying all the elements in 1d array

Suresh Jeevanandam wrote:[color=blue]
> Hi all,
> Lets say I have an array:
> from numarray import *
> a = array([ 6, 7, 8, 9, 10, 11, 12])
>
> I want to multiply out all the elements and get the result.
>
> r = 1.0
> for i in a:
> r = r*i
>
> Is there any faster, efficient way of doing this.[/color]

r = multiply.reduce (a)

--
Robert Kern
robert.kern@gma il.com

"In the fields of hell where the grass grows high
Are the graves of dreams allowed to die."
-- Richard Harter

[Tim Hochberg]

Re: numarray :: multiplying all the elements in 1d array

Mandus wrote:[color=blue]
> Tue, 20 Dec 2005 19:32:13 +0530 skrev Suresh Jeevanandam:
>[color=green]
>>Hi all,
>> Lets say I have an array:
>> from numarray import *
>> a = array([ 6, 7, 8, 9, 10, 11, 12])
>>
>> I want to multiply out all the elements and get the result.
>>
>> r = 1.0
>> for i in a:
>> r = r*i
>>
>> Is there any faster, efficient way of doing this.[/color]
>
>
> You can use multiply.reduce (a) (multiply is a function imported from
> numarray).
>
> With regular python you can also do:
>
> from operator import mul
> reduce(mul,a)
>
> This work even when 'a' is a plain python list.[/color]


Actually, they'll both work with a plain python list. Multiply.reduce is
much faster (see below) when operating on arrays, but somewhat slower
when operating on lists. I'd guess from the overhead of converting the
list to an array.

-tim

[color=blue][color=green][color=darkred]
>>> a = na.arange(10000 0)
>>> l = range(100000)
>>> t0 = time.clock(); na.multiply.red uce(a); print time.clock() - t0[/color][/color][/color]
0
0.0038896004939 2[color=blue][color=green][color=darkred]
>>> t0 = time.clock(); na.multiply.red uce(l); print time.clock() - t0[/color][/color][/color]
0
0.042208716471[color=blue][color=green][color=darkred]
>>> t0 = time.clock(); reduce(mul, a); print time.clock() - t0[/color][/color][/color]
0
0.0943455103931[color=blue][color=green][color=darkred]
>>> t0 = time.clock(); reduce(mul, l); print time.clock() - t0[/color][/color][/color]
0
0.0146099574108