Question

In R, I want to set dgCMatrix non-zero value to a vector.

For example:

Here is a dgCMatrix:

M
3 x 4 sparse Matrix of class "dgCMatrix"

[1,] . 1 . 1
[2,] . . 1 .
[3,] . . 1 .

And here is a vector:

a <- c(1,2,3,4)

And then , I want to set the non-zero value to the vector by column . The result will be :

[1,] . 2 . 4
[2,] . . 3 .
[3,] . . 3 .

Thanks .

Answer 1

This should be pretty generally efficient:

library(Matrix)
M <- Matrix(c(0,0,0,1,0,0,0,1,1,1,0,0), nc=4) ## Recreates your dgCMatrix
a <- 1:4

M %*% Diagonal(x=a)
# 3 x 4 sparse Matrix of class "dgCMatrix"
#             
# [1,] . 2 . 4
# [2,] . . 3 .
# [3,] . . 3 .

---

Edit:

If M has some values other than 0 and 1, you can instead use one of the following:

M <- M * 11:14  ## Alter M to test the following code 

as(M>0 | M<0, "dgCMatrix") %*% Diagonal(x=a)

as(!M==0, "dgCMatrix") %*% Diagonal(x=a)