Link the 2th column of a matrix to the first depending on another matrix.

Hello,

I'll just give a simple example to show what I want:

I have a matrix

A=[1,4;
   2,5;
   3,6];

And a long vector B with values 1,2 and 3 in an undefined order.

B = [1;3;1;2;1;3...];

From A and B I want to make one matrix C in which the first column is vector B and for the second column I want to let the values depend of the value of B. So if the value of B is 1 I want to get a 4, if 2 I want 5, if 3 I want to get 6. So each time the according value defined in matrix A.

Thanks in advance!

[Image Analyst]

You left the answer C out of your example for some reason.

[Klaas]

C should be: [1,4;3,6;1,4;2,5;1,4;3,6;...]

Answer 1

[Image Analyst]

How about this:

A=[1,4;
   2,5;
   3,6];
B = [1;3;1;2;1;3];
C = [B, A(B,2)]

C =
     1     4
     3     6
     1     4
     2     5
     1     4
     3     6

[Klaas]

THANKS!

[Klaas]

I still have a problem. This works for my example but in my script the numbers 1,2 and 3 from the example are decimal fraction. So I always get the 'Subscript indices must either be real positive integers or logicals.' error.

Someone who has a different solution?

[Image Analyst]

Let's say the number is 2.37. So you want row #2.37 from A. Can you explain exactly what it means to you to get the 2.37'th row from the second column of A?

Answer 2

[Roger Stafford]

Perhaps what you need is

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

This assumes that every value in B is to be found somewhere in the first column of A. If not, you will receive an error message.

[Image Analyst]

Oh, is that what he meant? I thought the B was the row numbers of A that he wanted to extract. I guess it's ambiguous but you might be right. Of course having the first column of A be row numbers didn't help clarify it, in fact it made it more ambiguous.