Linear indices from colon operator
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Any array (let's consider only 2D here) can be indexed using colon operator such
array(p1:p2,p3:p4)
How can one generate list of linear indices (for that particular array) from parameters [p1, p2, p3, p4]?
采纳的回答
Matt J
2024-11-14
[I,J]=ndgrid(p1:p2,p3:p4);
linear=sub2ind(size(array) , I,J);
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Steven Lord
2024-11-14
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2 个评论
Note that in general p1:p2 and p3:p4 when used a indices like that will refer to a rectangular block of that array. So in order to get the linear indices of the entire block you will need to provide SUB2IND with subscript indices for the entire block. One way to achieve this is using NDGRID:
array = randi(9,9,9);
p1 = 3;
p2 = 5;
p3 = 2;
p4 = 5;
[X,Y] = ndgrid(p1:p2,p3:p4);
Z = sub2ind(size(array),X,Y);
array(Z)
array(p1:p2,p3:p4)
sub2ind() processes the indexes in parallel. All of the indices must be the same size (or else scalars)
sub2ind([4 5],1:2,1:3)
K=createArray(size(array),Fill=sparse(0));
K(p1:p2,p3:p4)=1;
out=find(K); %linear indices
1 个评论
Matt J
2024-11-14
I would probably do instead,
K=createArray(size(array),Fill=sparse(false));
or maybe just use,
K=false(size(array))
depending on the expected size of the output.
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