How to indexing directly multiple row?

Question

balandong 2017-12-4

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/370986-how-to-indexing-directly-multiple-row

评论： balandong 2017-12-4

Dear all, I wonder how we can do direct indexing in compact form, for the following case? In this problem, i want to extract two rows for different columns. To achieve the objective, the following code was realize. But, the code is lengthy, and I wonder if we can simplify this.

Thanks in advance.

ShufleNperc=5;
randm_row_NUm=[randperm(ShufleNperc);randperm(ShufleNperc)]; % Row idx
randm_no=randi(50,ShufleNperc,ShufleNperc); % value to be extracted base on the row
vvvv=zeros(size(randm_row_NUm,1),ShufleNperc); % Prelocate memory
for x_v=1:ShufleNperc
vvvv(:,x_v)=randm_no((randm_row_NUm(:,x_v))',x_v);
end

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Answer 1

KL 2017-12-4

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https://ww2.mathworks.cn/matlabcentral/answers/370986-how-to-indexing-directly-multiple-row#answer_294604

编辑：KL 2017-12-4

在 MATLAB Online 中打开

use linear indices,

read this: https://www.mathworks.com/help/matlab/ref/sub2ind.html

With your example,

colInd = repmat(1:size(randm_no,2),2,1);
linind = sub2ind(size(randm_no),randm_row_NUm(:),colInd(:));
vvvv_simple = randm_no(linind);

you can reshape it if you want,

vvvv_simple = reshape(vvvv_simple,size(vvvv))

the result is the same for both methods,

>> vvvv
vvvv =
      48    48    33    38     3
       8    22    43    33     5
>> vvvv_simple
vvvv_simple =
      48    48    33    38     3
       8    22    43    33     5