indexing groups of elements in a vector in a certain way

Hi all,

I have two vectors A and B where they look like the following:

%vector A
A = [1 1 
    4 1
    5 1
    6 1
    5 2
    6 2
    7 2
    3 3 
    4 3
    5 3 
    3 3];
%vector B
B = [12 2
    34 3
    23 3
    56 2
    34 1
    54 1
    14 3
    76 2
    45 1
    76 1
    65 1];

The second column of each of these vectors corresponds to the index of each row. As can be seen, vector A has 3 main "groups". For each of these groups, there are 2 groups that corrspond to them in vector B. For example, for group 1 in vector A there are two groups 2 and 3 in vector B, and so on do forth.

It can be seen that in total vector B has 6 main groups. And here where I need help!

I want to reindex the rows of vector B without changing its elements order so that it contains 6 gorups and looks like:

%vector C
C = [12 1
    34 2
    23 2
    56 1
    34 3
    54 3
    14 4
    76 5
    45 6
    76 6
    65 6];

In this way, group 1 in vector A, has groups 1 and 2 in the new vector C. Group 2 in vectorA has groups 3 and 4 in vectro C. Group 3 in vector A has groups 5 and 6 in vector C.

Any help would be appreicted.

Thanks.

Answer 1

[Voss]

%matrix A
A = [1 1 
    4 1
    5 1
    6 1
    5 2
    6 2
    7 2
    3 3 
    4 3
    5 3 
    3 3];
%matrix B
B = [12 2
    34 3
    23 3
    56 2
    34 1
    54 1
    14 3
    76 2
    45 1
    76 1
    65 1];

[~,~,idx] = unique([A(:,2),B(:,2)],'rows','stable');

%matrix C
C = [B(:,1) idx];

disp(C)

    12     1
    34     2
    23     2
    56     1
    34     3
    54     3
    14     4
    76     5
    45     6
    76     6
    65     6

[LH]

thanks, that's great!

[Voss]

You're welcome!