title: Matrix multiplication with scattered NA values
body: <p>I'm looking to multiply two matrices together in R, one of which may contain randomly placed NA values (i.e., there's no reason they will be all in a row or column), but I still want an output like the example below:</p>
  
  <pre><code>Matrix 1
  [1,]      33        45    50
  [2,]       NA       NA    54
  
  Matrix 2
  [1,] A1               0.0000000        0.0000000
  [2,] 0.0000000        A2               0.0000000
  [3,] 0.0000000        0.0000000           A3
  
  
  Result
  [1,]      33*A1     45*A2          50*A3
  [2,]       NA       NA        (NA*0 +NA*0 +54*A3)=54*A3
  </code></pre>
  
  <p>Simply doing Matrix1%*%Matrix2 doesn't give what I want for the element in Row 2, Column 3 (it gives NA, which makes sense, but not sure how to do what I'd like it to do).  For my purposes, Matrix 2 will never have NA values, if that changes anything.</p>