Subset and replace rows and columns in a data.table
data.table, r
Solution
First of all - you do not need to, and should not (as a matter of good programming) use the `data.table` name inside `[.data.table`.
Secondly, you should avoid using column numbers whenever you can - this is a source of future headache, and should instead aim to use column names.
Finally, the way to change columns in `data.table`'s is to use the `:=` operator to modify in-place (see `?':='`).
Combining all of the above, this is what you should do:
test.dt[a < b, `:=`(a = 10 * a, b = 10 * b)]
Problem
I need to modify certain columns of specific rows of a data.table. I keep getting an error, "unused argument (with=F)". Does anyone know how to quickly deal with this? Below is an example using both data.frames and data.table. Thanks. ``` test.df <- data.frame(a=rnorm(100, 0, 1), b=rnorm(100, 0, 1), c=rnorm(100,0,1)) test.dt <- as.data.table(test.df) test.df[test.df$a<test.df$b,c(1,2)] <- 10* test.df[test.df$a<test.df$b,c(1,2)] test.dt[test.dt$a<test.dt$b, c(1,2), with=F] <- 10* test.dt[,c(1,2),with=F][test.dt$a<test.dt$b, c(1,2), with=F] ```