title: Sparse matrix to a data frame in R
body: <p>I have a sparse matrix </p>
  
  <pre><code>Formal class 'dgCMatrix' [package "Matrix"] with 6 slots
    ..@ i       : int [1:37674] 1836 2297 108 472 1735 1899 2129 2131 5 67 ...
    ..@ p       : int [1:3417] 0 2 8 22 25 35 44 45 45 47 ...
    ..@ Dim     : int [1:2] 3416 3416
    ..@ Dimnames:List of 2
    .. ..$ : chr [1:3416] "AAA" "AAE" "AAL" "AAN" ...
    .. ..$ : chr [1:3416] "AAA" "AAE" "AAL" "AAN" ...
    ..@ x       : num [1:37674] 1 1 1 1 1 1 1 1 1 1 ...
    ..@ factors : list()
  </code></pre>
  
  <p>What is a fast way to convert this matrix to a list as (except for a <code>for loop</code>):  </p>
  
  <pre><code>Origin Destination Weight
  AAA AAE 4
  AAL AAN 5
  </code></pre>
  
  <p>Note: I only need to get the Origin and Destination for Weight>0 </p>