[Numpy-discussion] help vectorizing something

Charles R Harris charlesr.harris@gmail....
Fri Oct 24 17:12:46 CDT 2008


On Fri, Oct 24, 2008 at 3:48 PM, Mathew Yeates <mat.yeates@gmail.com> wrote:

> Hi
> I  have 2 vectors A and B. For each value in A I want to find the location
> in B of the same value. Both A and B have unique elements.
>
> Of course I could something like
> For each index of A:
>        v =A[index]
>        location = numpy.where(B == v)
>
> But I have very large lists and it will take too long.
>

In [1]: A = array([1,2,3])

In [2]: B = array([5,1,3,0,2,4])

In [3]: i = B.argsort()

In [4]: Bsorted = B[i]

In [5]: indices = i[searchsorted(Bsorted,A)]

In [6]: indices
Out[6]: array([1, 4, 2])

Chuck
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