How to replace certain values in an array without using for-loop?

I have a very long array of length couple million. Say, A=[1;2;3;4;5;2;3;4;1;....] I have another array of different length (order of thousands to millions), we can call this second array B.

I would like to replace values in the first array with 0s if the value in A is present in B.

Currently, I have the following code to do it:

for i=1:length(B)
    A(A==B(i))=0;
end

However, I would like to get rid of for loop and make this as efficient as possible since the arrays that I am working with is very large, and this is only a very small portion of the entire code, which needs to be computable before I graduate.

Thank you in advance,

Answer 1

[Azzi Abdelmalek]

A(ismember(A,B))=0

[Louis]

Thanks, My understanding of the ismember command is that it is as computationally heavy as for loop. Any comments on this?

[Azzi Abdelmalek]

Look at this test

A=randi(1000,1000);
B=randi(1000,1000,1);
A1=A;
B1=B;
tic
for i=1:numel(B)
  A(A==B(i))=0;
end
time_with_loop=toc
%-------------------------------
tic
A1(ismember(A1,B1))=0;
time_with_ismember=toc

time_with_loop = 2.3960
time_with_ismember =0.0900

[Muthu Annamalai]

@Azzi shouldn't logical indexing work in this case?

A1( A1 == B1 ) = 0

[Image Analyst]

No, it won't. That will work only if they match up. It won't remove elements that occur anywhere in A or B.