Getting all diagonals from top right to bottom left in array

user_11558934 0
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I am trying to store all the diagonals in the matrix from the top right to the bottom left and store them in an array.

matrix = array([[2, 0, 0, 2],
                [3, 0, 0, 3],
                [3, 0, 0, 2],
                [0, 0, 0, 0]])

Expected ouptut

[
 [2],
 [0, 3],
 [0, 0, 2],
 [2, 0, 0, 0],
 [3, 0, 0],
 [3, 0],
 [0]
]

What I tried to do was this code: However, this will get me all the diagonals from top left to bottom right

def get_diags_lower_left(matrix):
    return [np.fliplr(matrix).diagonal(i) for i in range(-3, 4)][::-1]
matrix numpy arrays python
2 Answers

If you do not flip the matrix it works. Using:

def get_diags_lower_left(matrix):
    return [matrix.diagonal(i) for i in range(-3, 4)][::-1]

Will yield:

[array([2]),
 array([0, 3]),
 array([0, 0, 2]),
 array([2, 0, 0, 0]),
 array([3, 0, 0]),
 array([3, 0]),
 array([0])
]
user_148305340

A more generalized solution that works on any MxN matrix:

[matrix.diagonal(i) for i in range(-matrix.shape[0] + 1, matrix.shape[1])][::-1]

output:

[array([2]),
 array([0, 3]),
 array([0, 0, 2]),
 array([2, 0, 0, 0]),
 array([3, 0, 0]),
 array([3, 0]),
 array([0])]
user_122912950
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