# How to create an array out of a matrix based on criteria.

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DuckDuck am 18 Nov. 2014
Kommentiert: Thorsten am 19 Nov. 2014
Suppose i have a matrix of
a=[1,2;
1,3;
1,4;
2,12;
2,15;
5,7;
5,8;
6,98;
6.99;
7,8;
7,9;
7,11;
9,14;
9,16;
12,18;
14,20;
20,35;
98,102;
99,204;
204,300];
I want to create arrays arrays that will contain elements mentioned in the pair.
b=[1,2,3,4,12,15,18]
c=[5,7,8,9,14,16,20,35]
d=[6,98,99,102,204,300]
The idea is that if 2 is in a pair of 1, then every other element in pair with 2 will end up in the b array. So on and so forth for different categories, b,c,d,.... How can I achieve that kind of iteration in Matlab?
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### Akzeptierte Antwort

Thorsten am 18 Nov. 2014
Bearbeitet: Thorsten am 18 Nov. 2014
b = a(1,:); c = [];
for i = 2:size(a, 1)
if ~isempty(intersect(a(i,:), b))
b = union(b, a(i,:));
else
c = union(c, a(i,:));
end
end
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DuckDuck am 18 Nov. 2014
Bearbeitet: DuckDuck am 18 Nov. 2014
Thanks Thorsten, but this solution does not generalise. What if i'll have more b, c, d, e?
Thorsten am 19 Nov. 2014
Oh, you changed the question. That's not fair! (Just kidding.) The generalized solution is
b{1} = a(1,:);
for i = 2:size(a, 1)
bi = 1;
while bi <= numel(b) && isempty(intersect(a(i,:), b{bi}))
bi = bi + 1;
end
if bi <= numel(b) % append a(i,:) to b{bi}
b{bi} = union(a(i,:), b{bi});
else % create bi'th entry in cell b
b{bi} = a(i, :);
end
end
for bi = 1:numel(b)
disp(b{bi})
end

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