[Numpy-discussion] Selecting columns of a matrix

Keith Goodman kwgoodman at gmail.com
Wed Jun 21 09:13:54 CDT 2006


On 6/20/06, Bill Baxter <wbaxter at gmail.com> wrote:

> >>> a[:,num.where(v>0.5)[0]]
> array([[1, 2, 4],
>        [6, 7, 9]])
>
> I'll put that up on the Matlab->Numpy page.

That's a great addition to the Matlab to Numpy page.

But it only works if v is a column vector. If v is a row vector, then
where(v.A > 0.5)[0] will return all zeros. So for row vectors it
should be where(v.A > 0.5)[1].

Or, in general, where(v.flatten(1).A > 0.5)[1]




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