python - Find indices of a value in 2d matrix

Question

I have a matrix of the form,

mymatrix=[[1,2,3],[4,5,6],[7,8,9]]

I want to the get the index of, say for example, 9 which is at (2,2).

What I have tried to do so far.

for i,j in enumerate(mymatrix):
   for k,l in enumerate(j):
     if l==9:
         print i,k

Is there a better way of doing the same. Optimization, anyone? Thanks in advance.

Answer 1

If you convert mymatrix to a numpy array you can jsut use numpy.where to return the indices:

>>> import numpy as np
>>> mymatrix=[[1,2,3],[4,5,6],[7,8,9]]
>>> a = np.array(mymatrix)
>>> a
array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])
>>> b = np.where(a==9)
>>> b
(array([2]), array([2]))
>>> mymatrix=[[1,2,3],[9,5,6],[7,8,9]]
>>> a = np.array(mymatrix)
>>> a
array([[1, 2, 3],
       [9, 5, 6],
       [7, 8, 9]])
>>> b = np.where(a==9)
>>> b
(array([1, 2]), array([0, 2]))