Identifying ones in each row and creating a list in Python

June 15, 2023

I have an array A. I am identifying ones in each row except the row number itself and creating a list. For example, in A[0], the ones should be identified for locations 2,3,5 and not 0. I present the current and expected output.

import numpy as np

A=np.array([[1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0],
       [0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0],
       [1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0],
       [1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0],
       [0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0],
       [1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1, 0],
       [0, 1, 0, 1, 1, 0, 1, 0, 1, 1, 0, 1],
       [0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1, 0],
       [0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1],
       [0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1],
       [0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1, 0],
       [0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 1]])

output = []
for i, row in enumerate(A):
    ones_indices = np.where(row == 1)[0]
    other_rows = np.arange(A.shape[0])
    other_rows = np.delete(other_rows, i)
    output.append([[i], other_rows.tolist()])

print(output)

The current output is

[[[0], [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]], [[1], [0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]], [[2], [0, 1, 3, 4, 5, 6, 7, 8, 9, 10, 11]], [[3], [0, 1, 2, 4, 5, 6, 7, 8, 9, 10, 11]], [[4], [0, 1, 2, 3, 5, 6, 7, 8, 9, 10, 11]], [[5], [0, 1, 2, 3, 4, 6, 7, 8, 9, 10, 11]], [[6], [0, 1, 2, 3, 4, 5, 7, 8, 9, 10, 11]], [[7], [0, 1, 2, 3, 4, 5, 6, 8, 9, 10, 11]], [[8], [0, 1, 2, 3, 4, 5, 6, 7, 9, 10, 11]], [[9], [0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 11]], [[10], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 11]], [[11], [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10]]]

The expected output is

[[[0], [2,3,5]], [[1], [3,4,6]], [[2], [0,3,5]], [[3], [0, 1, 2, 4, 5, 6]], [[4], [1,3,6]], [[5], [0,2,3,7,8,10]], [[6], [1,3,4,8,9,11]], [[7], [5,8,10]], [[8], [5,6,7,9,10,11]], [[9], [6,8,11]], [[10], [5,7,8], [[11], [6,8,9]]]

>Solution :

The numpy approach would be to fill_diagonal, then to use where:

np.fill_diagonal(A, 0)

row, idx = np.where(A==1)  # np.where(A) if only 0/1

Output:

(array([ 0,  0,  0,  1,  1,  1,  2,  2,  2,  3,  3,  3,  3,  3,  3,  4,  4,
         4,  5,  5,  5,  5,  5,  5,  6,  6,  6,  6,  6,  6,  7,  7,  7,  8,
         8,  8,  8,  8,  8,  9,  9,  9, 10, 10, 10, 11, 11, 11]),
 array([ 2,  3,  5,  3,  4,  6,  0,  3,  5,  0,  1,  2,  4,  5,  6,  1,  3,
         6,  0,  2,  3,  7,  8, 10,  1,  3,  4,  8,  9, 11,  5,  8, 10,  5,
         6,  7,  9, 10, 11,  6,  8, 11,  5,  7,  8,  6,  8,  9]))

If you really want nested lists:

np.fill_diagonal(A, 0)

out = [[[i], np.where(a==1)[0].tolist()] for i, a in enumerate(A)]

Output:

[[[0], [2, 3, 5]],
 [[1], [3, 4, 6]],
 [[2], [0, 3, 5]],
 [[3], [0, 1, 2, 4, 5, 6]],
 [[4], [1, 3, 6]],
 [[5], [0, 2, 3, 7, 8, 10]],
 [[6], [1, 3, 4, 8, 9, 11]],
 [[7], [5, 8, 10]],
 [[8], [5, 6, 7, 9, 10, 11]],
 [[9], [6, 8, 11]],
 [[10], [5, 7, 8]],
 [[11], [6, 8, 9]]]