create a sparse matrix; given the indices of non-zero elements for creation of dummy variables of a categorical column of a large dataset

Question

I\'m trying to use a sparse matrix to generate dummy variables for a set of data with 5.8 million rows and two categorical columns.

The structure of the data is:

Answer 1

Why do you want a sparse matrix? For a dummy matrix you can also just use:

model.matrix(~ . + 0, data = df)

The 0 indicates no intercept and the . indicates that all categorical variables will be transformed. Be sure to set these variables as factors using as.factor() beforehand.

Answer 2

Try this:

spmat<-Matrix(0,nrow = 210000 ,ncol = 500,sparse = T)
locs<-Matrix(data=c(mydata$Var_1,mydata$Var_2),byrow=F,ncol=2)
spmat[locs]=1