Directly creating dummy variable set in a sparse matrix in R

Question

Suppose you have a data frame with a high number of columns(1000 factors, each with 15 levels). You\'d like to create a dummy variable data set, but since it would be too sp

Answer 1

This can be done slightly more compactly with Matrix:::sparse.model.matrix, although the requirement to have all columns for all variables makes things a little more difficult.

Generate input:

set.seed(123)
n <- 6
df <- data.frame(x = sample(c("A", "B", "C"), n, TRUE),
                 y = sample(c("D", "E"),      n, TRUE))

If you didn't need all columns for all variables you could just do:

library(Matrix)
sparse.model.matrix(~.-1,data=df)

If you need all columns:

fList <- lapply(names(df),reformulate,intercept=FALSE)
mList <- lapply(fList,sparse.model.matrix,data=df)
do.call(cBind,mList)