How to call index of vector in matrix?

Hello, I have: n-by-3 matrix A, and n-by-1 matrix B:

A=[ x1 y1 z1           
    x2 y2 z2
    x3 y3 z3
    x4 y4 z4
    .......
    xn yn zn ]

 B=[ 3           
     2
     7
     1
     ...
     n ]

B is index (labelling) matrix of A.

I wanna assign the vector A to vector B.

Ex:

(x1 y1 z1) assign to 1

(x3 y3 z3) assign to 3

......................

(xn yn zn) assign to n

- Instead of working with matrix A, I can work with "labelling" matrix B.

and then,

+ when I call 3 in matrix B, it will show the value (x3 y3 z3) from matrix A.

+ when I call 7 in matrix B, it will show the value (x7 y7 z7) from matrix A.

+ when I call [3,7] in matrix B, it will show the value matrix:

 A=[ x3 y3 z3           
     x7 y7 z7]

+ when I call n in matrix B, it will show the value (xn yn zn) from matrix A. ...............................................................

and vice versa ( I call (x3 y3 z3) from A, it will show 3 in B.....)

- How to write a code to call matrix A from matrix B , and vice versa?

(the number 3,2,7,1,....n: in matrix B is are arbitrary numbers and x1,x2,x3...xn : are the number)

Answer 1

[Image Analyst]

I don't know what it means to "call label 3" or B. Is B always 1,2,3,4 etc. - the natural counting numbers? Or can they be arbitrary numbers? If you have a number 3, and want to look up B(3) and use that as an index to get that row of A, you can simply do

out = A(B(3), :);

and if you want to "show" it, you can just leave off the semicolon:

out = A(B(3), :)

or use fprintf() :

fprintf('A(%d) = [%f, %f, %f]\n', B(3), A(B(3), 1), A(B(3), 2), A(B(3), 3));

or msgbox() or helpdlg():

message = sprintf('A(%d) = [%f, %f, %f]\n', B(3), A(B(3), 1), A(B(3), 2), A(B(3), 3));
uiwait(helpdlg(message));

Is that what you want?

[ha ha]

Sorry my question is not clear. Please see it again

[Image Analyst]

My answer stands. You can make it a function if you want

function out = GetValue(index, A)
out = A(index,:);

Since B is just 1,2,3,4,... we don't even need it.

[ha ha]

If I want to call back:

Example:

(x3 y3 z3) from A, it will show 3 in B.

(xn yn zn) from A, it will show n in B.

[x3 y3 z3

x5 y5 z5]

from A, it will show matrix [3,5] in B.

[Image Analyst]

To go in reverse like that, you can use ismember() to find out what row a particular 1-by-3 vector occurs in A, if in fact it does even occur.

[Jan]

@ha ha: Please use flags only to inform admins and editors about messages, which conflict with the terms of use of this forum. Thanks.

[ha ha]

Thanks.ok

Answer 2

[Andrei Bobrov]

A = [...
     6    -3     4
     7     8    -5
    -4     8     6
     7     1     8
     3     6     4
    -4    -4     5
    -2     0     5
     2     7     0
     8     6     4
     8     8    -3];

A2B(A,[6 -3 4;3 6 4])
A2B(A,[1;2])

here function A2B:

function out = A2B(A,in)
    if size(in,2) == 1
        out = A(in,:);
    else
        out = find(ismember(A,in,'rows'));
    end
end

[ha ha]

ok. your answer is also a solution. Thanks

index_matrix = find(ismember(A,B,'rows'));

This fuction is to find "index matrix" of each vector in matrix B from matrix A