[Numpy-discussion] Indexing with integer ndarrays

Robert Kern robert.kern at gmail.com
Sat Jun 13 20:17:30 EDT 2009

On Sat, Jun 13, 2009 at 19:11, Joe Kington<jkington at wisc.edu> wrote:
> 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.

I discuss this particular use case (well, a little different; we are
pulling out a thin slab around a horizon rather than a slice) here:


Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco

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