Repeat row of data table N times and join to another table in R-CodePudding

I have two data tables:

> dt1

 --- --- 
| V1| V2|
 --- --- 
|  a|  a|
|  a|  b|
|  a|  c|
|  b|  c|
|  c|  d|
 --- --- 

> dt2
 ------------------ 
|                id|
 ------------------ 
|  c(4, 98, 56, 32)|
 ------------------

dt2 has the following structure:

> str(dt2)
Classes ‘data.table’ and 'data.frame':  1 obs. of  1 variable:
 $ id:List of 1
  ..$ : int  4  98  56  32
 - attr(*, ".internal.selfref")=<externalptr>

I am looking for the most efficient way (if possible, based on the data.table approach) to add column values from the df2 as constant value to each row of the df1.
Expected result:

 --- --- ------------------ 
| V1| V2|                id|
 --- --- ------------------ 
|  a|  a|  c(4, 98, 56, 32)|
|  a|  b|  c(4, 98, 56, 32)|
|  a|  c|  c(4, 98, 56, 32)|
|  b|  c|  c(4, 98, 56, 32)|
|  c|  d|  c(4, 98, 56, 32)|
 --- --- ------------------

CodePudding user response：

Do you mean something like this?

dt1[, id:=dt2$id]

Output:

|V1 |V2 |id            |
|:--|:--|:-------------|
|a  |a  |c(4,98,56,32) |
|a  |b  |c(4,98,56,32) |
|a  |c  |c(4,98,56,32) |
|b  |c  |c(4,98,56,32) |
|c  |d  |c(4,98,56,32) |