fill in NAs for time variable - R

I have the following dataset:

Variable | Year | Value
A        | 2000 | 0.0003
B        | 2000 | 0.31
B        | 2001 | 0.09
C        | 2002 | 0.03

And I want to create a new dataset such as:

Variable | Year | Value  
A        | 2000 | 0.0003  
A        | 2001 | NA         
A        | 2002 | NA             
B        | 2000 | 0.31  
B        | 2001 | 0.09   
B        | 2022 | NA      
C        | 2000 | NA             
C        | 2001 | NA     
C        | 2002 | 0.03    

I have more columns in my actual dataset. Does anyone know of a quick way to do this?

Thanks!

You can use tidyr::complete()

tidyr::complete(df,Variable, Year)

Output:

  Variable  Year   Value
  <chr>    <dbl>   <dbl>
1 A         2000  0.0003
2 A         2001 NA     
3 A         2002 NA     
4 B         2000  0.31  
5 B         2001  0.09  
6 B         2002 NA     
7 C         2000 NA     
8 C         2001 NA     
9 C         2002  0.03  

Input:

structure(list(Variable = c("A", "B", "B", "C"), Year = c(2000, 
2000, 2001, 2002), Value = c(3e-04, 0.31, 0.09, 0.03)), class = "data.frame", row.names = c(NA, 
-4L))