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## vectorization

 From: David Pruitt Subject: vectorization Date: Tue, 3 Dec 2002 13:51:14 -0600

```In some work I'm now doing, I continually find the need to determine the
set of indices of vector A which contain elements of vector B - elements of
B will occur in A no more than once.  Here's an example of what my code
looks like:

# contrived example
# vector A
i_num = [1:100];
# vector B
v_num = [ 1 3 5 12 ];

lt = length(v_num);

for i = 1:lt

idx(i) = find( i_num == v_num(i) );

endfor;

In this example, idx would of course be 1,3,5,12.  So it's sort of a
two-dimensional "find".  I'll just bet I'm doing this the hard way.  Is
there another way without a for-loop?  For the cases I'm seriously
concerned with, the vectors contain 5,000 to 15,000 elements.

Thanks,
David

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