[SciPy-user] Efficiently scaling matrix rows

Christian Kristukat ckkart at hoc.net
Tue Nov 29 08:33:48 CST 2005


Neilen Marais wrote:
> Hi
> 
> I have a an n x 3 matrix (i.e. each row contains three elements). I want
> to scale each row by the element of a 1-d array. I.o.w, if I have 
> 
> arr = array([1., 2., 3., ....]),
> 
> I want to scale the first row of the matrix by arr[0], the second by
> arr[1], etc. ATM I'm doing this:
> 
> coefs = reshape(repeat(arr, 3), (-1, 3))
> mat = coefs*mat
> 
> Is there a more efficent (and potentially easier to read) way that does
> not require redundant copies of arr, while avoiding a slow python loop?

mat = mat*arr[:,NewAxis] should do the same.

Regards, Christian



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