get neighbors of a max value in 2D numpy array

Question

I have a 2D array of shape 10x10 and I need to find the neighbors of a maximum value in a 2D array. My code is:

import numpy as np array = np.random.randint(-10,10, size=(10,10)) max_index = np.argmax(array) def get_coordinate_i(value): i = 0 if value % 10 >= 1: i = value // 10 return i j = max_index - 10*get_coordinate_i(max_index) i = get_coordinate_i(max_index) def fun(i, j, array): arr = np.array([]) if i!=0 and j!=0 and i!=9 and j!=9: for val in range(-1,2): for val2 in range(-1,2): arr = np.append(arr, array[i+val][i+val2]) return np.reshape(arr, (3,3))

Though, it is not working properly every time.

FBruzzesi · Accepted Answer · 2020-03-19 11:22:35Z

Avoiding loops:

a = np.random.randint(0,100, (10,10)) x, y = np.unravel_index(a.argmax(), a.shape) box = a[np.max([x-1, 0]):np.min([x+1, 9])+1, np.max([y-1, 0]):np.min([y+1, 9])+1]

Remark that this does not account for multiple occurrence of the max value, and argmax() method stops at first occurance.

Rohit Sohlot · Accepted Answer · 2020-03-19 11:15:53Z

you can calculate the i,j and the matrix around the max. value in a different sorter way.

import numpy as np array = np.random.randint(-10,10, size=(10,10)) max_index = np.argmax(array) j = max_index%10 i = max_index//10 if j==0: matrix_around_max =array[i-1:i+2,j:j+2] elif i ==0: matrix_around_max = array[i:i+2,j-1:j+2] elif i==0 and j==0: matrix_around_max = array[i:i+2,j:j+2] else: matrix_around_max = array[i-1:i+2,j-1:j+2]

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