Merge two dgCMatrix sparse matrices of different size in R

Question

How can I merge two large (around 500k columns and rows) sparse matrices of formal class dgCMatrix with different sizes (both columns and rows wise) in R?

Answer 1

One strategy would be to convert the matrices back to the same size and then add them.

A <- sparseMatrix(8, 8, x = 1)
B <- sparseMatrix(c(1,3,5), c(3,6,3), x = c(1,4,1))

You can access the indices of matrix B with summary(B) and then just recreate the matrix with sparseMatrix(i,j,x,dims) like you would a normal subsetting operation in R:

> summary(B)
5 x 6 sparse Matrix of class "dgCMatrix", with 3 entries 
  i j x
1 1 3 1
2 5 3 1
3 3 6 4

B <- sparseMatrix(i = summary(B)$i, j = summary(B)$j, x = summary(B)$x, dims = dim(A))

Then you can just add the matrices:

A = A + B