converting a dgCMatrix to data frame

I would like to convert a sparse matrix into a data frame of the type (row,column, value). I have found questions such as that in the question start with row,column,value and create a sparse matrix. I want the inverse, and I cannot use the as.matrix function, because the matrix is too large. Here is a small example.

r = c(1,2,2,3,3) c = c(4,1,2,3,5) v = c(1,2,1,3,1) a = sparseMatrix(i=r,j=c,x=v) 3 x 5 sparse Matrix of class "dgCMatrix" [1,] . . . 1 . [2,] 2 1 . . . [3,] . . 3 . 1 

Can I get a data.frame

 r c v 1 1 4 1 2 2 1 2 3 2 2 1 4 3 3 3 5 3 5 1 

Thank you

1 Answer

You can use

b = as.data.frame(summary(a)) # i j x # 1 2 1 2 # 2 2 2 1 # 3 3 3 3 # 4 1 4 1 # 5 3 5 1 

If you need the same order as in your example, you can use

b = b[order(b$i),] # i j x # 4 1 4 1 # 1 2 1 2 # 2 2 2 1 # 3 3 3 3 # 5 3 5 1 

Another alternative, though not quite as neat, is to use

b = as(a, "dgTMatrix") cbind.data.frame(r = b@i + 1, c = b@j + 1, x = b@x)