# Filtering nested lists with python conditions

how are you?

I have a distance matrix and need to perform a filter based on another list before applying some functions.

The matrix has 10 elements that represent machines and the distances between them, I need to filter this list by getting only the distances between some chosen machines.

``````matrix = [[0, 1, 3, 17, 24, 12, 18, 16, 17, 15],
[1, 0, 2, 2, 5, 6, 13, 11, 12, 10],
[3, 2, 0, 1, 6, 12, 18, 12, 17, 15],
[17, 2, 1, 0, 3, 12, 17, 15, 16, 14],
[24, 5, 6, 3, 0, 1, 24, 22, 23, 21],
[12, 6, 12, 12, 1, 0, 12, 10, 11, 9],
[18, 13, 18, 17, 24, 12, 0, 3, 4, 5],
[16, 11, 12, 15, 22, 10, 3, 0, 1, 2],
[17, 12, 17, 16, 23, 11, 4, 1, 0, 1],
[15, 10, 15, 14, 21, 9, 5, 2, 1, 0]]
``````

The list used for filtering, for example, is:

``````filter_list = [1, 2, 7, 10]
``````

The idea is to use this list to filter the rows and the indices of the sublists to get the final matrix:

``````final_matrix = [[0, 1, 18, 15],
[1, 0, 13, 10],
[18, 13, 0, 5],
[15, 10, 5, 0]]
``````

That’s what I tried:

``````final_matrix = []

for i in range(0, len(filter_list)):
for j in range(0,len(filter_list[i])):
a = filter_list[i][j]
final_matrix .append(matrix[a-1])
print(final_matrix)
``````

This is because the filter_list can have sublists. I get it:

``````final_matrix = [[0, 1, 3, 17, 24, 12, 18, 16, 17, 15],
[1, 0, 2, 2, 5, 6, 13, 11, 12, 10],
[18, 13, 18, 17, 24, 12, 0, 3, 4, 5],
[15, 10, 15, 14, 21, 9, 5, 2, 1, 0]]
``````

I could not remove the spare elements.

### >Solution :

You forgot to filter by column ids.

``````final_matrix = [[matrix[row-1][col-1] for col in filter_list] for row in filter_list]
``````