Replacing elements of a Matrix meeting conditional

Hi, I have two matrixes and wish to replace the first column of matrix A, with elements of the fourth column of matrix B, but just in the case the elements of the first columns of A and B are equal.

I tried the following, but its probably not correct. Can someone help me out?

for j=1:size(A,1)

    if A(j,1)==B(:,1);
        A(j,1)=B(:,4);
    end
end

Answer 1

[Fangjun Jiang]

A=rand(14,5);A(:,1)=1:14;
B=rand(5,4);B(:,1)=10:-2:2;B(:,4)=10*B(:,1);

[Dummy,IndexA,IndexB]=intersect(A(:,1),B(:,1));
A(IndexA,1)=B(IndexB,4)

[Patricia]

Thanks. But still not working. My problem is that the "matching" element of matrix B, doesn´t necessarily is on the same line as the element of matrix A.

[Fangjun Jiang]

Paulo's answer will do it. Don't accept an answer before the problem is solved. Providing an example data will always help.

[Patricia]

Ja, first time using this 'answers'... I'm still on it. The arrays are A (1401X5) and B (137X4). The values on first column variate from 1 to 1400; in 1 step size for A, and randomly for B.

[Patricia]

'randomly' but still between 1 and 1400

Answer 2

[Paulo Silva]

%sample arrays
a=randi([1 6],4,4);
b=randi([1 6],4,4);
e=a(:,1)==b(:,1);   %find what elements are equal in first columns
a(e,1)=b(e,4)       %replace the elements

[Patricia]

'eq' won´t work if the matrixes have <> size

Answer 3

[Patricia]

Just worked it out! I had a similar problem once... had forgotten :) Used:

idx=ismember(A:,1), B(:,1)); B = [B A(idx,4)];

so I added a column in B, which is also OK. Thanks again!

[Fangjun Jiang]

Nice! I also updated my answer. It's similar, for your reference.