title: Co-occurrence matrix using SAC?
body: <p>I have the following data frame 'x'</p>
  
  <pre><code>id,item,volume
  a,c1,2
  a,c2,3
  a,c3,2
  a,c4,1
  a,c5,4
  b,c6,6
  b,c1,2
  b,c3,1
  b,c2,6
  b,c4,4
  c,c2,5
  c,c8,6
  c,c9,2
  d,c1,1
  e,c3,7
  e,c2,3
  e,c1,2
  e,c9,5
  e,c4,1
  f,c1,7
  f,c3,1
  </code></pre>
  
  <p>The first column is the id of a customer, the second column is the id of an item that customer bought and the third column is the number of those items bought. I'm trying to create a co-occurrence matrix which is a square matrix with 8 rows and columns, 8 being the number of distinct items.</p>
  
  <pre><code>n = length(unique(x$cid))
  </code></pre>
  
  <p>Could this be done through a SAC paradigm? For every id, I need to update the above matrix by adding +1 for every combination. For example for user 'b' with items c1,c2,c3,c4,c6, the 1st row in the matrix for columns 2,3,4 &amp; 6 should be incremented by 1 and so on for all users. I'm unable to cast it into this framework. Any help much appreciated.</p>