This code works for a numpy 2D matrix array:
mat = np.array([[1, 3], [2, 5]]) # numpy matrix
n = 2 # n
n_largest_mat = np.sort(mat, axis=None)[-n:] # n_largest
tf_n_largest = np.zeros((2,2), dtype=bool) # all false matrix
for x in n_largest_mat:
tf_n_largest = (tf_n_largest) | (mat == x) # true-false
n_largest_elems = mat[tf_n_largest] # true-false indexing
This produces a true-false n_largest matrix indexing that also works to extract n_largest elements from a matrix array