[R] Matrix multiplication with scattered NA values

[arun]

Hi,
Not sure if this is what you wanted:
 mat1<- as.matrix(read.table(text="
      33        45    50
      NA       NA   54
",sep="",header=FALSE))
mat2<- as.matrix(read.table(text="
24                0.0000000        0.0000000
0.0000000        14                0.0000000
0.0000000 0.0000000        10
",sep="",header=FALSE))
 mat1%*%mat2
 #     V1  V2  V3
#[1,] 792 630 500
#[2,]  NA  NA  NA

library(Matrix)
mat1m<- as(mat1,"dgCMatrix")
 mat2m<- as(mat2,"dgCMatrix")
tcrossprod(mat1m,mat2m)
#2 x 3 sparse Matrix of class "dgCMatrix"
#                
#[1,] 792 630 500
#[2,]  NA  NA 540
A.K.



>Hi, 
>
>I'm looking to multiply two matrices together, 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: 
>
>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 
>
>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.