How to construct an undirected graph by reading edge by edge from a text file

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TR RAO
TR RAO 2017-9-6
回答： TR RAO 2017-9-28
Suppose I have a list of edges in a text file(dont know how many edges are there in a text file). I have to create an undirected graph from it. Finally I have to construct first order transition probability matrix from that graph. for example for the edges={a,b}, {a,c}, {a,d}, the transition matrix is [0 1/3 1/3 1/3;1 0 0 0; 1 0 0 0;1 0 0 0]
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TR RAO
TR RAO 2017-9-6
编辑：TR RAO 2017-9-6
Kindly find the text file here. I have to form a graph by reading edges in the text file. And from that graph I have to form a first order transition matrix.

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回答（2 个）

Josh Meyer
Josh Meyer 2017-9-6
You can use textscan to read the text file into a cell array, with the first entry listing the source nodes and the second entry listing the target nodes. Then you can create the graph directly from the cell array columns.
fid = fopen('textfile.txt');
C = textscan(fid,'%s%s')
fclose(fid);
G = graph(C{1},C{2})
If the file lists duplicate edges (for an undirected graph a->b and b->a is a duplicate edge, so the example file you provided contains duplicates) you'll need to trim those away first. One method is to convert to a char array, sort the edges, find the unique rows, then convert back to a cell array:
C = cell2mat([C{1} C{2}]);
C = unique(sort(C,2),'rows');
C = num2cell(C)
G = graph(C(:,1),C(:,2))
TR RAO
TR RAO 2017-9-28
clc; clear; fileID = fopen('C:\Users\TR RAO\Desktop\rao1.txt','r'); C = textscan(fileID, '%s %s'); fclose(fileID); C1 =cell2mat(C{1,1}); C2 =cell2mat(C{1,2}); CC = [C1,C2] s=C1;t=C2; nodes = unique(CC); n_nodes = size(nodes,1) S0=eye(n_nodes); adjacency_matrix = false(n_nodes); for idx = 1:size(C1,1) adjacency_matrix(C1(idx)==nodes,C2(idx)==nodes) = 1; end adjacency_matrix n_elements = sum(adjacency_matrix,2); transition_matrix = adjacency_matrix./repmat(n_elements, 1, n_nodes); transition_matrix(isnan(transition_matrix)) = 0; P=transition_matrix;
I am reading a list of edges from a textfile. For small file with six edges it is forming a transition matrix. but for large file of 50000 edges it is giving the following error. Error using cat Dimensions of matrices being concatenated are not consistent.
Error in cell2mat (line 83) m{n} = cat(1,c{:,n});
Error in readingfile1 (line 14) C1 =cell2mat(C{1,1});

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