如何从多维列表中的元素获取索引？

Question

Here is what I'm trying to do:

board = [[0, 1, 2, 3] , [4, 5, 6, 7] , [8, 9, 10, 11] , [12, 13, 14, 15,]].index("8")
print(board)

I get the error:

ValueError '8' is not in the list

How can I get the index from this element?

Answer 1

You can iterate and return the index value:

next((i for i, x in enumerate(board) if n in x), 'not found')

---

board = [[ 0 , 1 , 2 , 3 ] , [ 4 , 5 , 6 , 7 ] , [ 8 , 9 , 10 , 11 ] , [ 12 , 13 , 14 , 15 , ]]

n = 8
print(next((i for i, x in enumerate(board) if n in x), 'not found'))

This prints:

2

In case you want all indices of the value, switch to a list comprehension:

[i for i, x in enumerate(board) if n in x]

Answer 2

I don't think there is a built in way to do it. I would do it using numpy:

import numpy as np
board = [[ 0 , 1 , 2 , 3 ] , [ 4 , 5 , 6 , 7 ] , [ 8 , 9 , 10 , 11 ] , [ 
12 , 13 , 14 , 15 , ]]
b=np.asarray(board)
print(np.argwhere(b==8))

result: array([[2, 0]])

Answer 3

this assumes there is only one occurrence of an element.

board = [[ 0 , 1 , 2 , 3 ] , [ 4 , 5 , 6 , 7 ] , [ 8 , 9 , 10 , 11 ] , [ 12 , 13 , 14 , 15 ]]

var = [ele for ele in board if 8 in ele][0]

# check if element is not present in the list
if len(var) == 0:
    print('-1')

else:
    print('index: (', board.index(var), var.index(8), ')')

output:

index: ( 2 0 )

Answer 4

What index in python does is find the element match which in your case are all lists and you are trying to match a int

You can use numpy to get the location

import numpy as np
board = [[ 0 , 1 , 2 , 3 ] , [ 4 , 5 , 6 , 7 ] , [ 8 , 9 , 10 , 11 ] , [ 12 , 13 , 14 , 15 ]]
np.where(np.array(board) == 8)

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

which is basically board[2][0]