How to create data.table with different size of columns

Question

I create data.table like this.

DT = data.table(A=c(1,2,3), B=c(1,2,3,4,5))

But I get this result.

   A B
1: 1 1
2: 2 2
3: 3 3
4: 1 4
5: 2 5

but I'd like to get this.

   A B
1: 1 1
2: 2 2
3: 3 3
4: NA 4
5: NA 5

How can I create data.table with different size?

Answer 1

We keep the vector of unequal length in a list ('lst'), then loop through the list elements, append NA at the end and convert to data.table.

lst <- list(A=c(1,2,3), B=c(1,2,3,4,5))
DT <- setDT(lapply(lst, `length<-`, max(lengths(lst))))[]
DT
#    A B
#1:  1 1
#2:  2 2
#3:  3 3
#4: NA 4
#5: NA 5