[Numpy-discussion] Indexing with integer ndarrays

Joe Kington jkington at wisc.edu
Sat Jun 13 20:11:32 EDT 2009

Hi folks,

This is probably a very simple question, but it has me stumped...

I have an integer 2D array containing 3rd dimesion indicies that I'd like to
use to index values in a 3D array.

Basically, I want the equivalent of:

> output = np.zeros((ny,nx))
> for i in xrange(ny):
>     for j in xrange(nx):
>         z = grid[i,j]
>         output[j,i] = bigVolume[j,i,z]

Where grid is my 2D array of indicies and bigVolume is my 3D array.

I've read the numpy-user and numpybook sections on indexing with an integer
ndarray, but I'm still not quite able to wrap my head around how it should
work.  I'm sure I'm missing something obvious (I haven't been using numpy
particularly long).

If it helps anyone visualize it, I'm essentially trying to extract
attributes out of a seismic volume along the surface of a horizion.

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