Access matrix by list of matrix indices in Numpy

Question

I have a list of matrix indices and want to access a matrix by these indices.

Example:

indices = [(2, 0), (2, 1), (2, 2)]
mat = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
mat[indices] = 0

This should result in [[1, 2, 3], [4, 5, 6], [0, 0, 0]], but unfortunately I always get "list indices must be integers, not list".

EDIT

As user2357112 suggests in his comment I tried the following now:

mat = numpy.array(mat)
indices = numpy.array(indices)
mat[indices] = 0

But unfortunately the whole matrix is filled with 0 now.

Answer 1

indices is a regular list of tuples and can't be used to get an element of your regular mat. What you can do is iterate over your list to get your indices:

for x, y in indices:
    mat[x][y] = 0

If you want to use numpy methods, you need to create a numpy array. Indeed, np.array structure allows to use tuple to access to an element:

mat = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
for item in indices:
    mat[item] = 0

Answer 2

You can use zip(*indices) to access a numpy array by an indices list:

import numpy as np

indices = [(2, 0), (2, 1), (2, 2)]
mat = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])

>> mat[zip(*indices)]
array([7, 8, 9])
>> mat[zip(*indices)] = 0
>> mat
array([[1, 2, 3],
       [4, 5, 6],
       [0, 0, 0]])