Question of a vlookup equivalent in matlab

I dont think a vlookup function exists in matlab, but can you guys give me some pointers on how to replicate it? I have a matrix A and vector B, and I want to extract the rows in matrix A into a new matrix C if the A(:,1) is found in vector B. Will I need a loop?

I created C = A( A(:,1) == B(1:end) ,:), but I have a matrix dimesions disagreement. Is there a way to loop through each element of B?

[Matt Kindig]

I'm not sure I really understand your question. Can you post some sample data and your expected output?

[Mike]

So if A =[ 1 2 3 4 ; 4 9 8 0 ; 8 7 8 9] and B is a vector = [ 1 8] I want a matrix C such that C = [ 1 2 3 4; 8 7 8 9]. Is this better?

Answer 1

[Cedric]

Try this:

 >> id = ismember(A(:,1), B)
 id =
     1
     0
     1

 >> C = A(id,:)
 C =
     1     2     3     4
     8     7     8     9

[Mike]

Works. Thanks again.

[Cedric]

You're welcome.

[Ben Petschel]

I think this will give the wrong answer if A and B aren't sorted. An alternative solution is

[~,idx] = ismember(B,A(:,1));
C = A(idx,:)

[Andrei Bobrov]

[la,idx] = ismember(B,A(:,1));
C = A(idx(la),:);

[Cedric]

Yes, I assumed them to be sorted based on the numeric example, but I shouldn't have! Thank you for the comments.