How to generate a logical indexing based on any element of a multiple line matrix

Hi all,

I am struggling to produce a logical matrix based on a multiple line matrix. According to the example on the code below:

%
% A = [1048575x1];
% B = [40x1]; contains indexes to evaluate each line of A. If any element
% of A == any element of B, I would like to mark a logical YES (1). Elseif
% NO (0);
% As a result I would like to replace by "-9999" where is a logical truth
% I tried the following routine, but it is wrong:
for i=1:1:length(B)
if A == stops_start_id(i);
 A = -9999;
end
end
 %

Thank you for your time,

Answer 1

[Guillaume]

Using a loop for this is extremely inefficient. Use ismember instead:

A(ismember(B, A)) = -9999; %that's it, all done

The correct syntax for your loop would have been:

for ib = 1:numel(B)  %prefer numel or size over length. no need to put increment when one
   A(A == B(ib)) = -9999;
end

or even simpler:

for b = B' %for automatically iterates over columns, so b takes all the values of B in turn.
   A(A == b) = -9999;
end

Basically, don't use if if you're using logical arrays. In any case, as I said don't use a loop.