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How to extract matrix with different starting index for each row?

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I am not sure how to extract from a matrix a smaller matrix with different starting index for each row.
For example,
Original matrix (4x5):
[1 2 3 4 5]
[6 7 8 9 10]
[11 12 13 14 15]
[16 17 18 19 20]
Desired output (4,3):
[2 3 4]
[6 7 8]
[13 14 15]
[17 18 19]
where the starting index for each row is [2,1,3,2]
Thank you!

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Accepted Answer

Fangjun Jiang
Fangjun Jiang on 20 Oct 2020
%%
Orig=transpose(reshape(1:20,5,[]))
StartPos=[2;1;3;2];
Wid=3;
row=repmat((1:size(Orig,1))',1,Wid);
col=StartPos+(0:Wid-1);
index=sub2ind(size(Orig),row,col);
out=Orig(index)

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