Efficient multiplication of columns in a data frame

Question

I have a large data frame in which I am multiplying two columns together to get another column. At first I was running a for-loop, like so:

for(i in 1:nrow(d         


        

Answer 1

A data.table solution will avoid lots of internal copying while having the advantages of not spattering the code with $.

 library(data.table)
 DT <- data.table(df)
 DT[ , new := column1 * column2]