Extract specific values from a 3D matrix?

Question

Ivan Gufler 2023-1-31

编辑： Fangjun Jiang 2023-1-31

Hello,

I have a 3d matrix (call it A) of the following dimension: 9000, 9, 2. From this matrix I want to update two values in the following positions:

row_index=[4000, 3000]

col_index=[4,5]

Basically I want:

A(row_index, col_index,:)=B

where B is a 2x1 vector.

I could do this within a loop but I'd like to vectorize this operation.

Does anybody have a suggestion on how to do this in an efficient way?

Answer 1

Fangjun Jiang 2023-1-31

编辑：Fangjun Jiang 2023-1-31

A(sub2ind(size(A),row_index,col_index))=B

For example

A=false(6,6,6);
row_index=[4, 3];
col_index=[4,5];
B=[true;true];
A(sub2ind(size(A),row_index,col_index))=B;
sum(A,'all')
ans = 2