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Can this be vectorized?

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Patrick Mboma
Patrick Mboma 2014-10-30
评论： Patrick Mboma 2014-10-30
Dear all,
I have two vectors A and B of respective sizes na and nb, with na>=nb. All elements in B are unique while the elements in A are not. But all elements in A are in B. I would like to create a mapping between A and B and one way to do that is as follows:
A=nan(na,1);
for ii=1:nb
A(A==B(ii))=ii;
end
This works well be becomes prohibitively expensive for large na. And so my question is whether there is a way of getting rid of the for loop and/or creating this mapping differently.
Thanks,
P.

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Andrei Bobrov
Andrei Bobrov 2014-10-30
编辑：Andrei Bobrov 2014-10-30
[lc,ii] = ismember(A,B);
A(lc) = ii(lc);
or with nan
out = ii;
out(~lc) = nan;
or jast (with zeros)
out = ii;
  1 个评论
Patrick Mboma
Patrick Mboma 2014-10-30
Thanks Andrei,
I ended up implementing it as
[~,out] = ismember(A,B);
where out is exactly what I am looking for (given that all the elements in A are in B).

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