Construct adjacency matrix from input dataset graph file using matlab editor

Question

How can I construct adjacency matrix from input dataset graph file, which has the following data:

The first line of the dataset file, represents the number of nodes and edges resp. The following lines represent node1 and node2 denoting an edge existing between them For example: amazon.graph dataset file contains the following

Below is the file amazon.graph
4 6 // number of nodes and edges
0 1 // edge between node 0 and 1
1 3
2 3
1 2
0 2
0 3

This data is contained in a file named "amazon.graph". I need help with a matlab function that can read the file and build adjacency matrix from the dataset file

Answer 1

Use sparse to build the matrix:

x = [4 6
     0 1
     1 3
     2 3
     1 2
     0 2
     0 3]; %// data

adjMatrix = sparse(x(2:end,1)+1, x(2:end,2)+1, 1, x(1,1), x(1,2));

This produces a sparse matrix. You can convert to full form if needed:

adjMatrix = full(adjMatrix);

In your example, this gives

adjMatrix =

     0     1     1     1     0     0
     0     0     1     1     0     0
     0     0     0     1     0     0
     0     0     0     0     0     0

---

To make the graph symmetric (undirected):

s = max(x(1,1), x(1,2)); %// take largest dimemsion
adjMatrix = sparse(x(2:end,1)+1, x(2:end,2)+1, 1, s, s); %// now matrix is square
adjMatrix = adjMatrix | adjMatrix.'; %'// apply "or" with transpose to make symmetric
adjMatrix = full(adjMatrix); %// convert to full if needed

---

If you have the data in a file, you can read it into the variable x using textread . For example, if the file data.txt contains the text

4     6
0     1
1     3
2     3
1     2
0     2
0     3

just use

x = textread('data.txt');

Then you can apply the above to generate the adjMatrix from x .