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[MATLAB] I need any help for this problem

Asked by Jung Hyun on 29 Dec 2012

I tried to solve this problem, but I could not implement.

Could you help me anything for this?

[Problem]

Mat1 ||| Mat2 ||| Mat3
1 2 ||| 1 3 ||| 2 6
1 3 ||| 2 6 ||| 2 5
2 4 ||| 3 1 ||| 3 1
3 1 ||| 3 5 ||| 5 2
4 5 |||

When there are 3 matrices(for example above), I want to get this result for the intersection rows in [column1 column2 matrixnumber] form.

The result for above example would be

1 3 1
1 3 2
2 6 2
2 6 3
3 1 1
3 1 2
3 1 3

It would be OK if the result is in the form [column1 column2 firstmatrix secondmatrix, ...]

1 3 1 2
2 6 2 3
3 1 1 2 3

For this problem, I want to use at most one for-loop.

Do you have any idea for this?

Thank you in advance.

1 Comment

Image Analyst on 29 Dec 2012

Explain the first row. How is the intersection of 1 & 2 with 1 & 3 with 2 & 6 equal to 1 3 1??? The 1 intersects in Mat1 and Mat2 (because both Mat1 and Mat2 have a 1 in them), and the 2 intersects with Mat1 and Mat3, but there is no intersection of any number with all three matrices (in that first row). In that first row, there is no number that is in all three matrices.

And Mat1 has 5 rows while Mat2 and Mat3 have only 4 rows. How are you getting an output of 3 1 1 for the 5th row. And how are you generating a 6th and 7th row for your output when no matrix has that many rows?

Jung Hyun

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2 Answers

Answer by Image Analyst on 29 Dec 2012

I have no idea what you want or how you got that output, but take a look at ismember(), and intersect() and similar functions.

0 Comments

Image Analyst
Answer by Andrei Bobrov on 29 Dec 2012
Edited by Andrei Bobrov on 29 Dec 2012
M = {Mat1,Mat2,Mat3};
M1 = cat(1,M{:});
n = cellfun(@(x)size(x,1),M(:));
n1 = [0;cumsum(n)];
n2 = zeros(n1(end),1);
n2(n1(1:end-1) + 1) = 1;
n2 = cumsum(n2);
[a,~,c] = unique(M1,'rows');
n3 = accumarray(c,n2,[],@(x){x});
t = cellfun(@numel,n3) > 1;
out = [num2cell(a(t,:),2), n3(t)]; 

way with intersect

M = {Mat1,Mat2,Mat3};
n = nchoosek(1:numel(M),2);
k = [];
for j1 = 1:size(n,1)
    a = intersect(M{n(j1,:)});
    k = [k; [a ones(size(a,1),1)*n(j1,:)]];
end
[b,~,c] = unique(k(:,1:end-2),'rows');
k1 = accumarray(c,(1:numel(c))',[],@(x){x});
out = [num2cell(b,2), cellfun(@(x)unique(k(x,end-[1 0])),k1,'un',0)];

1 Comment

Image Analyst on 29 Dec 2012

I would have been nice if you'd included the code to generate Mat1, etc. so others could try it easily.

Andrei Bobrov

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