How can I change for-loop into matrix way?

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

[Jan]

Are you sure, that your 2nd loop is "for j=1000"?

[icdi]

Yes. The second loop needs much more iterations than the first one.

[Matt J]

@icdi Jan means, shouldn't you have this instead:

for j=1:1000

With " for j=1000" the inner loop is only doing 1 iteration for every i.

[icdi]

Oh it was my mistake. you are right. It's for j=1:1000.

I edited it. Thanks for letting me know that.

[Matt J]

We also need to know the sizes of all the variables.

[icdi]

A is 101 X 1000, and A(1,:) is given.

B is 15 X 1.

C is 15 X 15 X 3.

E is 101 X 1.

F is 100 X 1000.

Thanks!

[Matt J]

And D is 3x1?

Also, is the loop working in its current form? As far as I can see, there is no reason why

find(C(B==A(i,j),:,D==E(i))>F(i,j),1)

should be gauranteed to give a number between 1 and 15, as the code assumes it will. This will only be true if there is a unique m with B(m)=A(i,j) and a unique n with D(n)=E(i).

[icdi]

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]

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?

Answer 1

[Matt J]

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

[icdi]

Thanks! Your code works very well and saves me time. Thanks again.