[Numpy-discussion] flatindex
Stefan van der Walt
stefan@sun.ac...
Fri Jun 1 10:29:54 CDT 2007
Hi Tobias
On Thu, Jan 08, 2004 at 08:35:07PM +0100, Tobias Knopp wrote:
^^^^^^^^^^^^
Sorry I'm only answering now, but your mail took 3.5 years to arrive ;)
> I was looking for a method to find the indices of the smallest element
> of an 3-dimensional array a. Therefore i used
>
> a.argmax()
>
> The problem was, that argmax gives me a flat index. My question is, if
> there is a build-in function to convert the flat index back to a
> multidimensional one. I know how to write such a procedure but was
> curious if one exists in numpy.
numpy.unravel_index:
"""
Convert a flat index into an index tuple for an array of given shape.
e.g. for a 2x2 array, unravel_index(2,(2,2)) returns (1,0).
Example usage:
p = x.argmax()
idx = unravel_index(p,x.shape)
x[idx] == x.max()
Note: x.flat[p] == x.max()
Thus, it may be easier to use flattened indexing than to re-map
the index to a tuple.
"""
Cheers
Stéfan
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