[Numpy-discussion] yet another indexing question
Fabrice Silva
silva@lma.cnrs-mrs...
Fri Oct 14 08:51:38 CDT 2011
Le vendredi 14 octobre 2011 à 08:04 -0400, Neal Becker a écrit :
> suppose I have:
>
> In [10]: u
> Out[10]:
> array([[0, 1, 2, 3, 4],
> [5, 6, 7, 8, 9]])
>
> And I have a vector v:
> v = np.array ((0,1,0,1,0))
>
> I want to form an output vector which selects items from u where v is the index
> of the row of u to be selected.
>
> In the above example, I want:
>
> w = [0,6,2,8,4]
>
> I can't seem to find a syntax that does this.
>
> Now, more importantly, I need the result to be a reference to the original array
> (not a copy), because I'm going to use it on the LHS of an assignment. Is this
> possible?
What about np.where?
http://docs.scipy.org/doc/numpy/reference/generated/numpy.where.html
w = np.where(v, u[1], u[0])
if you may want to have more than two options (more than two lines for
u), then np.choose may be more appropriate
http://docs.scipy.org/doc/numpy/reference/generated/numpy.choose.html
--
Fabrice Silva
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