how to arrange an array elemets to unique pairs?

for example, X={'a1', 'b2', 'c3', 'd4'};

I want to rearrange X as below:

A={'a1'; 'a1'; 'a1'; 'b2';'b2'; 'c3' } B={'b2'; 'c3'; 'd4' ;'c3';'d4';'d4'}

that means A, B:

'a1' 'b2'

'a1' 'c3'

'a1' 'd4'

'b2' 'c3'

'b2' 'd4'

'c3' 'd4'

Then how to get A and B according to X?

Answer 1

[Azzi Abdelmalek]

X={'a1', 'b2', 'c3', 'd4'};
ii=1:numel(X)
jj=nchoosek(ii,2)
A=X(jj(:,1))'
B=X(jj(:,2))'

Answer 2

[Image Analyst]

It sounds like you want to generate A and B from X, rather than take an existing A and B and stitch them together horizontally like you'd do with C=[A,B].

But I can't figure out any general rule for generating A and B except to just manually do it from individual elements:

% This is what we're starting with:
X={'a1', 'b2', 'c3', 'd4'}
% This is what we want to generate
% A={'a1'; 'a1'; 'a1'; 'b2';'b2'; 'c3' } 
% B={'b2'; 'c3'; 'd4' ;'c3';'d4';'d4'}
% Now, create A
A = [X(1); X(1); X(1); X(2); X(2); X(3)]
% Now, create B
B = [X(2); X(3); X(4); X(3); X(4); X(4)]

And you get A and B from X just like you wanted:

A = 
    'a1'
    'a1'
    'a1'
    'b2'
    'b2'
    'c3'
B = 
    'b2'
    'c3'
    'd4'
    'c3'
    'd4'
    'd4'

If you want it generalized to some different number of strings (rows), then you'll need to fill us in on what the rule for creating the order is, because I can't figure out any general rule. And, of course the rule for generating A is different than the rule for generating B so we'd need both rules.

[vx2008]

Thank you for your reply.

We can use 'nchoosek' to do this work better.

Thank you at all.