Summing submatrices of numpy boolean arrays
I have a boolean matrix 11x51
a
. On this I do this operation in Matlab to get a boolean matrix of size 10x50
.
a = logical(a(1:end-1,1:end-1) + a(2:end,1:end-1) + a(1:end-1,2:end) + a(2:end,2:end))
I want to do this in python. I tried this: -
a = np.zeros([11,51], dtype=bool)
a=a[0:-2,0:-2] + a[1:-1,0:-2] + a[0:-2,1:-1] + a[1:-1,1:-1]
I ended up with a matrix 9x49
and I'm not sure if it does the expected operation.
Can anyone point out the error?
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2 answers
Using slicing
, this would be -
a_out = (a[:-1,:-1] + a[1:,:-1] + a[:-1,1:] + a[1:,1:]).astype(bool)
Since it is a
already a boolean array, we can skip the conversion bool
.
An example of a run on MATLAB -
>> a = logical([
1, 1, 0, 1, 1, 0
0, 1, 0, 0, 0, 0
1, 1, 0, 1, 1, 1
0, 0, 0, 0, 1, 0
0, 0, 1, 0, 1, 1
0, 0, 0, 1, 1, 0]);
>> a(1:end-1,1:end-1) + a(2:end,1:end-1) + a(1:end-1,2:end) + a(2:end,2:end)
ans =
3 2 1 2 1
3 2 1 2 2
2 1 1 3 3
0 1 1 2 3
0 1 2 3 3
>> logical(a(1:end-1,1:end-1) + a(2:end,1:end-1) + ...
a(1:end-1,2:end) + a(2:end,2:end))
ans =
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
0 1 1 1 1
0 1 1 1 1
An example of a NumPy run -
In [160]: a # Same data as in MATLAB sample
Out[160]:
array([[ True, True, False, True, True, False],
[False, True, False, False, False, False],
[ True, True, False, True, True, True],
[False, False, False, False, True, False],
[False, False, True, False, True, True],
[False, False, False, True, True, False]], dtype=bool)
In [161]: (a[:-1,:-1] + a[1:,:-1] + a[:-1,1:] + a[1:,1:])
Out[161]:
array([[ True, True, True, True, True],
[ True, True, True, True, True],
[ True, True, True, True, True],
[False, True, True, True, True],
[False, True, True, True, True]], dtype=bool)
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