I would like to create a new column inside my data table, this column being a vector of values; but I am getting the following error:
DT = data.table(x=rep(c("a","b"),c(2,3)),y=1:5)
>
> DT
x y
1: a 1
2: a 2
3: b 3
4: b 4
5: b 5
> DT[, my_vec := rep(0,y)]
Error in rep(0, y) : invalid 'times' argument
My expected result is:
> DT
x y my_vec
1: a 1 0
2: a 2 0 0
3: b 3 0 0 0
4: b 4 0 0 0 0
5: b 5 0 0 0 0 0
Is there a way to do that?
The syntax is a little cumbersome, but you can do this:
DT[, my_vec := list(list(rep(0, y))), by = y]
DT
# x y my_vec
#1: a 1 0
#2: a 2 0,0
#3: b 3 0,0,0
#4: b 4 0,0,0,0
#5: b 5 0,0,0,0,0
It is not clear whether you need a list as my_vec or a vector. If it is the latter, we group by sequence of rows, replicate the 0 with 'y' and paste the elements together within each group.
DT[, my_vec := paste(rep(0, y), collapse=' ') , 1:nrow(DT)]
DT
# x y my_vec
#1: a 1 0
#2: a 2 0 0
#3: b 3 0 0 0
#4: b 4 0 0 0 0
#5: b 5 0 0 0 0 0
