How To: Multi-level subindexing

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Gabriel Stanley
Gabriel Stanley 2023-2-7
评论： Gabriel Stanley 2023-2-7
I'm tryig to achieve a proper 1-line ndex/sub-indexing operation, but have thus far failed to get the syntax right
ArrayA = sparse(100,100000);
ArrayA(randi(100*100000,[7000 1])) = (82-36).*rand(7000,1)+36;
[ArrayAFull(:,1),ArrayAFull(:,2),ArrayAFull(:,3)] = find(ArrayA);
ArrayB = sparse(100,100000);
ArrayB(randi(100*100000,[7000 1])) = (90-30).*rand(7000,1)+30;
[ArrayBFull(:,1),ArrayBFull(:,2),ArrayBFull(:,3)] = find(ArrayB);
[~,IdxA,IdxB] = intersect(ArrayAFull(:,[1,2]),ArrayBFull(:,[1,2]),'stable','rows');
t1 = ArrayBFull(ArrayBFull(IdxB,1)==1,:); %This is where things go sour
%The next two lines get me the actually desired matrix
t2 = ArrayBFull(IdxB,:);
t2 = t2(t2(:,1)==1,:);
isequal(t1,t2); %false
Is it possible to compress the t2 lines into a single line, or no?

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采纳的回答

Walter Roberson
Walter Roberson 2023-2-7
Yes, it is, but it is fairly ugly to do so. You can call upon subsref() manually, possibly having used substruct() to help build the appropriate structure.
It is usually a lot easier to use a helper function. For example,
SelectRowWhere = @(expression, where) expression(expression(:,1)==where,:);
t2 = SelectRowWhere(ArrayBFul(IdxB,:), 1)
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Walter Roberson
Walter Roberson 2023-2-7
The two line version would typically be faster, as calling an anonymous function is notably slower than calling a non-anonymous function.

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