Can I change iteration value in following for loop?

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Jake 2022-12-21

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https://ww2.mathworks.cn/matlabcentral/answers/1882412-can-i-change-iteration-value-in-following-for-loop

评论： Jan 2022-12-22

采纳的回答： Jan

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Suppose I have the following code.

nf1 = 3; nf2 = 4;
panel_no = 1:12;
R_vx = rand(144,1);
for i = 1:nf1
    for ii = 1:nf2
        for iii = 1 : length(panel_no)
            velx(iii,:, ii, i) = [panel_no(iii), R_vx(iii)];
        end
    end
end
velx

My goal is to create a 4D double matrix, and velx provides the right structure. However, it only includes the first 12 values of R_vx (for obvious reasons, of course). If the second iteration of the for loop starts from 13 for R_vx, and the third one from 25 and so on, I'd get the desired matrix. Is there a way to implement this? TIA!

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采纳的回答

Jan 2022-12-21

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1882412-can-i-change-iteration-value-in-following-for-loop#answer_1133207

在 MATLAB Online 中打开

Maybe you mean:

nf1 = 3; nf2 = 4;
panel_no = 1:12;
R_vx = rand(144,1);
velx = repmat([panel_no.', reshape(R_vx, 12, 12)], 1, 1, nf1, nf2);

It is hard to guess the wanted output based on a not working code.

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Jan 2022-12-21

在 MATLAB Online 中打开

@James: "Although I cannot think of a rational way to implement it in order to get the desired output." - As far as I understand this means, that the shown code does not do, what you want. Posting the code repeatedly does not explain anything, if it does not work.

"have the first 12 elements of R_vx in first "set" (velx(:,:,1,1)) and the second 12 elements in the second "set" (velx(:,:,2,1))" - This is what my code does. But R_vx = (1:3:142).' contains 4 blocks of 12 elements only. Therefore my code creates the output as [12 x 2 x 4] array. Where do the elements of the 4th dimension come from?

I'm still trying to find out by questions for clarifications, what the wanted output is. Maybe you can create it manually and posting it as MAT file?

Another bold guess:

velx = zeros(length(panel_no), 2, nf2, nf1);  % Pre-allocate
c = 0;
for i = 1:nf1
    for ii = 1:nf2
        for iii = 1 : length(panel_no)
            c = c + 1;
            velx(iii,:, ii, i) = [panel_no(iii), R_vx(c)];
        end
    end
end

Does this create the wanted output?

Jake 2022-12-22

Yes! The bold guess works! :)

Introducing c was the missing link. Thank you so much!

Jan 2022-12-22

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@James: Fine. Then without a loop:

nf1 = 3; nf2 = 4;
panel_no = 1:12;
R_vx = rand(144,1);
A = [repmat(panel_no, 1, numel(R_vx)/numel(panel_no)); R_vx.'];
B = reshape(A, 2, 12, 4, 3);
C = permute(B, [2, 1, 3, 4]);