How can I change for-loop into matrix way?

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icdi 2021-6-7

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/849845-how-can-i-change-for-loop-into-matrix-way

评论： icdi 2021-6-8

I'd like to vectorize the for-loop below, but cannot come up with any idea. Could you help me?

        for i=1:100
            for j=1:1000
            A(i+1,j)= B(find(C(B==A(i,j),:,D==E(i))>F(i,j),1));
            end
        end

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icdi 2021-6-8

编辑：icdi 2021-6-8

Yes all of your points are right.

D is 3x1. For all i and j, A(i,j) is supposed to have one of elements of B, and E(i) also has one of elements of D. So this code can give the series of numbers between 1 and 15.

Matt J 2021-6-8

编辑：Matt J 2021-6-8

So the elements of B and D are all unique? Also, what is supposed to happen if find() returns empty [], i.e., if

C(B==A(i,j),k,D==E(i)) < F(i,j)

for all k=1...15?

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采纳的回答

Matt J 2021-6-8

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/849845-how-can-i-change-for-loop-into-matrix-way#answer_719570

This gives some speed-up.

%Fake Data
m=100;n=1000;  
B=rand(15,1); 
D=rand(3,1);
A=B(randi(15,m+1,n));
E=D(randi(3,m+1,1)); 
C=rand(15,15,3); 
F=0.3*ones(size(A));
%Original version
tic;
for i=1:m
    for j=1:n
    A(i+1,j)= B(find(C(B==A(i,j),:,D==E(i))>F(i,j),1));
    end
end
toc
Elapsed time is 0.372233 seconds.
A1=A;
%Proposed version
tic;
locD=(1:3)*(D==E.');
for i=1:m
   
    Ai=A(i,:);
    Ei=E(i);
    Fi=F(i,:);
    [~,locB]=ismember(Ai,B);
    [~,idx]=max( C(locB,:,locD(i))>Fi(:) ,[],2); 
    A(i+1,:)= B(idx);
  
end
toc
Elapsed time is 0.050406 seconds.
A2=A;
isequal(A1,A2)
ans = logical
   1