Filtering an adjacency matrix in matlab

Question

I have got a nx3 adjacency matrix that contains nodes in the first two dimension and the correspondant weight in the third dimension. I want to filter the matrix for specific thresholds (for nodes indexing). For example, I want to keep the adjacency matrix for nodes smaller than 10.000, 20.000, etc. Which is the most efficient way to do so in matlab? I tried to do the following, find the index which correspond to nodes:

counter = 1;
for i=1: size(graph4, 1)
   if (graph4(i,1) >30000) | (graph4(i,2) >30000)
      bucket(counter) = i;
      counter=counter+1;
   end
end

Is that a working code? Does it give your desired result? What is bucket? And what is the purpose of the counter? — Stewie Griffin, Jul 15 '14 at 11:45
Basically I want to store the indexes that after I ll remove from graph4 matrix. — snake plissken, Jul 15 '14 at 11:58

Stewie Griffin · Accepted Answer · 2014-07-15T12:02:27.473

Suppose the adjacency matrix is A as given below:

A =    
    8    1    6
    3    5    7
    4    9    2
   11    4    9
    6    8   10
    7   12    5
   17   10   15
   12   14   16
   13   18   11

If you want both column 1 and column 2 to be less than a value, you can do:

value = 10;
T = A(A(:,1) < value & A(:,2) < value, :)
T =    
    8    1    6
    3    5    7
    4    9    2
    6    8   10

The following line seems to give the same results as your sample code (but it doesn't seem like it fits your description.

value = 10000;
bucket = find((A(:,1)>value) | A(:,2)>value)

I guess you made a mistake and want to increment the counter above the bucket-line and initialize it as counter = 0 before the loop? As it is now, it will be one more than the number of elements in the bucket-list.

Yes exactly i want both column to be lower than 7. – snake plissken Jul 15 '14 at 11:59 — snake plissken, Jul 15 '14 at 11:59

Filtering an adjacency matrix in matlab

1 Answers1