[Numpy-discussion] computing average distance
Charles R Harris
charlesr.harris@gmail....
Mon Nov 3 11:48:47 CST 2008
On Sun, Nov 2, 2008 at 12:23 PM, Paul Rudin <paul@rudin.co.uk> wrote:
>
> I'm experimenting with numpy and I've just written the code below, which
> computes the thing I want (I think). Self.bits is an RxRxR array
> representing a voxelized 3d model - values are either 0 or 1. I can't
> help thinking that's there must be a much nicer way to do it. Any
> suggestions?
>
>
> centre = numpy.array(scipy.ndimage.measurements.center_of_mass(self.bits))
>
> vectors = []
> for x in xrange(R):
> for y in xrange(R):
> for z in xrange(R):
> if self.bits[x,y,z]:
> vectors.append([x,y,z])
>
> vectors = numpy.array(vectors)
> distances = numpy.sqrt(numpy.sum((vectors-centre) ** 2.0, axis=1))
> av_dist = numpy.average(distances)
>
Try nonzero:
In [5]: bits = np.random.random_integers(0,1, size=(3,3,3))
In [6]: vectors = nonzero(bits)
In [7]: vectors
Out[7]:
(array([0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2]),
array([0, 0, 0, 1, 1, 2, 2, 0, 0, 1, 2, 2, 0, 0, 1, 1, 2, 2]),
array([0, 1, 2, 0, 1, 0, 2, 0, 2, 0, 1, 2, 0, 1, 0, 2, 0, 2]))
The arrays three arrays contain the x, y, z indices.
Chuck
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