CODEWITHSUNDEEP
numpy
Maximilian
Maximilian

Reputation: 8530

Generate a 'closeness to center' matrix in numpy

I think this should be easy, but I'm not sure of an efficient way to do it.

I'd like to build a matrix in numpy that has the cityblock / manhattan closeness to the center of the matrix, in numpy, for any odd size.

For a size of 5, the output would be: 

array([[0, 1, 2, 1, 0],
       [1, 2, 3, 2, 1],
       [2, 3, 4, 3, 2],
       [1, 2, 3, 2, 1],
       [0, 1, 2, 1, 0]])

What's the best way of doing this? Thanks

Upvotes: 1

Views: 127

Answers (1)

Divakar
Divakar

Reputation: 221774

Easy and efficient with broadcasting -

def closeness_manhattan(N):
    r = np.arange(N)
    a = np.minimum(r,r[::-1])
    return a[:,None] + a

Sample runs -

In [14]: closeness_manhattan(4)
Out[14]: 
array([[0, 1, 1, 0],
       [1, 2, 2, 1],
       [1, 2, 2, 1],
       [0, 1, 1, 0]])

In [15]: closeness_manhattan(5)
Out[15]: 
array([[0, 1, 2, 1, 0],
       [1, 2, 3, 2, 1],
       [2, 3, 4, 3, 2],
       [1, 2, 3, 2, 1],
       [0, 1, 2, 1, 0]])

Upvotes: 3

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