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Align digraph EdgeCData with correct edges

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Alex Wooten
Alex Wooten on 26 Jun 2021
Commented: Alex Wooten on 30 Jun 2021
I am working with an adjacency matrix which I am displaying in a digraph, and I have a corresponding matrix that contains additional information about my data, which I would like to use for the edge colors. The problem is, the EdgeCData property expects a vector, and in the conversion, the data is no longer aligned properly.
A = [1 1 0 0 0; 0 0 0 0 1; 0 1 0 0 1; 1 0 0 0 0; 0 0 1 1 0]; %adjacency matrix
CData = [.85 .1 0 0 0; 0 0 0 0 .2; 0 .5 0 0 .65; .3 0 0 0 0; 0 0 .45 1 0]; %color data
CDataVec = nonzeros(CData); %convert to vector for EdgeCData property (misaligns data)
colormap jet
caxis([0 1])
G = digraph(A);
DG = plot(G);
DG.EdgeCData = CDataVec;
c = colorbar;
My understanding is that adjacency matrices map onto digraphs such that the row ID is directed to the column ID (eg data in row 4, column 1 of adjacency matrix 'A' would have node 4 connecting to node 1 in the digraph). The edge color I would like in this case is 0.3 (since that is the value at row 4, column 1 in CData) but instead it is 1. How can I get all of the color data to line up with the proper edges?

Accepted Answer

Asvin Kumar
Asvin Kumar on 30 Jun 2021
Edited: Asvin Kumar on 30 Jun 2021
You need to transpose the CData matrix before passing it into nonzeros.
nonzeros generates a list of non-zero elements by traversing the input 2D matrix in column-major form. However, the digraph generates a list of edges from the adjacency matrix in row-major form.
Try this code:
A = [1 1 0 0 0; 0 0 0 0 1; 0 1 0 0 1; 1 0 0 0 0; 0 0 1 1 0]; %adjacency matrix
CData = [.85 .1 0 0 0; 0 0 0 0 .2; 0 .5 0 0 .65; .3 0 0 0 0; 0 0 .45 1 0]; %color data
CDataVec = nonzeros(CData.'); %convert to vector for EdgeCData property
colormap jet
caxis([0 1])
G = digraph(A);
DG = plot(G);
DG.EdgeCData = CDataVec;
c = colorbar;
% Compare the order of the following two arrays:
CDataVec
CDataVec = 8×1
0.8500 0.1000 0.2000 0.5000 0.6500 0.3000 0.4500 1.0000
G.Edges.EndNodes
ans = 8×2
1 1 1 2 2 5 3 2 3 5 4 1 5 3 5 4
  1 Comment
Alex Wooten
Alex Wooten on 30 Jun 2021
Great thank you for the in-depth explanation! I was hoping the answer would be something simple like that.

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