Converting *.rds into *.csv file
Solution 1:
Sparse matrice often cannot be converted directly into a dataframe.
This answer might be very resource intensive, but it might work by converting the sparse matrix to a normal matrix first and then saving it to a csv. Try this:
write.csv(as.matrix(data),file="file.csv")
This solution is not efficient and might crash R, so save your work prior.
As a general comment, this csv-file will be huge, so it might be more helpful to use more efficient data storage like a database engine.