Take a 4x1 and 4x2 matrix and create a 4x2 matrix instead of a 4x4

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charles purwin
charles purwin 2020-4-30
评论： Ameer Hamza 2020-5-2
I have the following data that I am trying to put into an array, but I am not finding the right combination of bracketing to make this work:
% state_rotate is fixed to these values of 4x2 double array
state_rotate=[1,3;1,3;2,4;2,4];
% state_indx gets set in other parts of the code; it can be 1;1;1;1 to 2;2;2;2 only using 1 or 2 as digits
state_indx = [1;2;2;1];
% take and using state_index (1 or 2 value) which state "wins"
win_state(1)=state_rotate(1,state_indx(1));
win_state(2)=state_rotate(2,state_indx(2));
win_state(3)=state_rotate(3,state_indx(3));
win_state(4)=state_rotate(4,state_indx(4));
For this example the end result is
win_state = [1;3;4;2]
What i would like to do is use a more compact notation to assign values to win_state. Something along the lines of:
win_state=state_rotate(:,state_indx(:));
This notation gives me a 4x4 matrix with what appears to be the correct values diagonally. I would like to not use a for loop but do the right type of matrix calculations.
I am still learning matlab, and it seemed maybe reshape could help, but I don't want to create the larger matrix since if I scale this code this matrix can get rather large.
Thanks!

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Ameer Hamza
Ameer Hamza 2020-4-30
Here is the compact notation using sub2ind()
state_rotate=[1,3;1,3;2,4;2,4];
state_indx = [1;2;2;1];
idx = sub2ind(size(state_rotate), 1:size(state_rotate,1), state_indx.');
win_state = state_rotate(idx);

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