How do you delete a column by name in data.table?

Question

To get rid of a column named \"foo\" in a data.frame, I can do:

df <- df[-grep(\'foo\', colnames(df))]

However, once df

Answer 1

I simply do it in the data frame kind of way:

DT$col = NULL

Works fast and as far as I could see doesn't cause any problems.

UPDATE: not the best method if your DT is very large, as using the $<- operator will lead to object copying. So better use:

DT[, col:=NULL]

Answer 2

You can also use set for this, which avoids the overhead of [.data.table in loops:

dt <- data.table( a=letters, b=LETTERS, c=seq(26), d=letters, e=letters )
set( dt, j=c(1L,3L,5L), value=NULL )
> dt[1:5]
   b d
1: A a
2: B b
3: C c
4: D d
5: E e

If you want to do it by column name, which(colnames(dt) %in% c("a","c","e")) should work for j.