how to arrange an array elemets to unique pairs?

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vx2008
vx2008 on 24 Dec 2015
Commented: vx2008 on 25 Dec 2015
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?

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Accepted Answer

Azzi Abdelmalek
Azzi Abdelmalek on 24 Dec 2015
Edited: Azzi Abdelmalek on 24 Dec 2015
X={'a1', 'b2', 'c3', 'd4'};
ii=1:numel(X)
jj=nchoosek(ii,2)
A=X(jj(:,1))'
B=X(jj(:,2))'

More Answers (1)

Image Analyst
Image Analyst on 24 Dec 2015
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.
  1 Comment
vx2008
vx2008 on 25 Dec 2015
Thank you for your reply.
We can use 'nchoosek' to do this work better.
Thank you at all.

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