Heli wrote:
> I have a 3d numpy array containing true/false values for each i,j,k. The
> size of the array is a*b*c.
>
> for each cell with indices i,j,k; I will need to check all its neighbours
> and calculate the number of neighbour cells with true values.
>
> A cell with index i,j,k has the following neighbours :
>
> n1 with indices [i-1,j,k] if i>0 ; cell with i=0 does not have any n1
> neighbour. (left neighbour)
I'm not a numpy expert, so the following may be less elegant than and not as
efficient as possible; it may also be outright wrong ;)
With that caveat:
$ cat neighbours.py
import numpy
from collections import deque
def print_int(a):
print(numpy.array(a, dtype=int))
# generate sample data
numpy.random.seed(42)
SHAPE = (3, 3, 3)
DIMENSIONS = len(SHAPE) # dimensions
a = numpy.random.random(SHAPE) < .5
b = numpy.zeros(SHAPE, dtype=int)
print("input data:")
print_int(a)
print("")
# actual calculation
full = slice(None, None, None)
left = slice(None, -1, None)
right = slice(1, None, None)
ileft = deque([left] + [full] * (DIMENSIONS-1))
iright = deque([right] + [full] * (DIMENSIONS-1))
for i in range(DIMENSIONS):
b[ileft] += a[iright]
b[iright] += a[ileft]
ileft.rotate()
iright.rotate()
print("number of neighbours:")
print(b)
$ python neighbours.py
input data:
[[[1 0 0]
[0 1 1]
[1 0 0]]
[[0 1 0]
[0 1 1]
[1 1 0]]
[[1 1 0]
[1 1 1]
[1 0 1]]]
number of neighbours:
[[[0 3 1]
[3 2 2]
[1 3 1]]
[[3 2 2]
[3 5 3]
[3 2 3]]
[[2 3 2]
[3 4 3]
[2 4 1]]]
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