Sorting specific values of one matrix into another
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Hey there,
so i got this problem where I have a dataset of "values" pointing to each other, as in this example:
A=[1 2;
4 5;
5 6;
2 7;
7 3;
3 1;
6 4];
1 -> 2 -> 7 -> 3 -> 1
Value 1 is associated with 2 and value 2 associated with 7 and so on, until I am back at value 1.
Now I am trying to get only those values into another set of data like seen in matrix B.
B=[1 2;
2 7;
7 3;
3 1];
So far I have tried out multiple things using for and while loops with the function "find" to locate the values I am looking for and trying to pick those out of Matrix A into B. Is there mybe an easiert way to accomplish this task?
Thx in advance!
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Accepted Answer
Guillaume
on 24 Aug 2019
It looks like you're dealing with graphs. Initially I thought you were dealing with directed graphs but your comment saying that [2, 7] is the same as [7, 2] would imply that it's undirected graphs. Either way, you're better off using matlab's graph functions.
A=[1 2;
4 5;
5 6;
2 7;
7 3;
3 1;
6 4];
g = graph(A(:, 1), A(:, 2)); %or use digraph for directed graph
g.Nodes.ID = (1:height(g.Nodes))'; %add ID to nodes so that it's preserved
plot(g, 'NodeLabel', g.Nodes.ID); %to visualise the graph
Now, it's also not clear what you want, it looks like you want to extract connected components from your graph but it's not clear why you just want one of them and not the other. Anyway, to get the connected components:
[bins, binsize] = conncomp(g, 'OutputForm', 'cell');
components = cellfun(@(b) subgraph(g, b), bins, 'UniformOutput', false)
The B you wanted is the largest of the two graph, so maybe:
[~, largestindex] = max(binsize);
Bgraph = components{largestindex};
B = Bgraph.Nodes.ID(Bgraph.Edges.EndNodes)
figure; plot(Bgraph, 'NodeLabel', Bgraph.Nodes.ID)
compsimplified = cellfun(@simplify, components, 'UniformOutput', false)
More Answers (2)
KALYAN ACHARJYA
on 24 Aug 2019
Edited: KALYAN ACHARJYA
on 24 Aug 2019
A=[1 2;4 5;5 6;2 7;7 3;3 1;6 4];
k=A(1,2);
idx_data=[];
m=1;
while k~=A(1,1)
[idx c1]=find(A(:,1)==k);
idx_data(m)=idx;
m=m+1;
k=A(idx,2);
end
result=A([1,idx_data],:)
Result:
result =
1 2
2 7
7 3
3 1
Note: Assuming that A(1,2) is not equal to A(1,1), in given A matrix, you can modify it, and make it more simple.
3 Comments
KALYAN ACHARJYA
on 24 Aug 2019
Edited: KALYAN ACHARJYA
on 24 Aug 2019
Requested you to read your original question please
This is the logic of your original question, the loop it going on until get the initial value A(1,1)
Now you changed the direction (may be in both ways), that also can be possible, with slight modification
A=[1 2;4 5;5 6;7 2;7 3;3 1;6 4];
What would be the expected result for this case, or show us the pictorial figure as I have shown for privious case?
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