How to indexing directly multiple row?

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balandong
balandong 2017-12-4
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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KL
KL 2017-12-4
编辑：KL 2017-12-4
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
  1 个评论
balandong
balandong 2017-12-4
Hi KL, Thanks for the quick reply. Seems your solution ignore the usage of for loops ad more neat.
Thank you

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