Error when using Pivot_wider function in R?

I am using pivot_wider function on the following sample data but look like I am missing something here as the output are producing NA's with not rightly placing data into its respective column. Any suggestion, please?

library(tidyverse)
set.seed(123)
DF <- data.frame(Date = seq(as.Date("1991-01-01"), 
                        to = as.Date("2000-12-31"), 
                        by = "year"), 
                        Parameter = rep(c("A","B"), times = 10),
                        Value = runif(10,1,50)) %>% 
                        pivot_wider(names_from = Parameter, values_from = Value)

Output

> print(DF)
# A tibble: 10 × 3
   Date       A         B        
   <date>     <list>    <list>   
 1 1991-01-01 <dbl [2]> <NULL>   
 2 1992-01-01 <NULL>    <dbl [2]>
 3 1993-01-01 <dbl [2]> <NULL>   
 4 1994-01-01 <NULL>    <dbl [2]>
 5 1995-01-01 <dbl [2]> <NULL>   
 6 1996-01-01 <NULL>    <dbl [2]>
 7 1997-01-01 <dbl [2]> <NULL>   
 8 1998-01-01 <NULL>    <dbl [2]>
 9 1999-01-01 <dbl [2]> <NULL>   
10 2000-01-01 <NULL>    <dbl [2]>

I think you've got an error in how you're generating your sample data. Apologies if this isn't what you're looking for, but here's how I think you can get your desired output:

EDIT: @s_pike provided the same solution below, about a minute before me, with an explanation of what we both changed. Sorry for omission and thanks to them for that- included now for clarity.

The problem is in your call to rep(). You're currently repeating A and B ten times, for a total of 20 values in the Parameter column. Because you're providing a vector of 10 dates, it will be recycled to match the length of Parameter. Because A and B are replicated one after the other, each date has the same Parameter value when Date is recycled: the cause of the duplication.

If instead you change the call to: Parameter = c(rep("A",10),rep("B",10)) each value in Date gets a Parameter of both A and B, so there are no duplications. See below:

> set.seed(123)
> DF <- data.frame(Date = seq(as.Date("1991-01-01"),
                            to = as.Date("2000-12-31"), 
                            by = "year"), 
                 Parameter = c(rep("A",10),rep("B",10)),
                 Value = runif(10,1,50))

> DF
         Date Parameter     Value
1  1991-01-01         A 15.091298
2  1992-01-01         A 39.626952
3  1993-01-01         A 21.039869
4  1994-01-01         A 44.267853
5  1995-01-01         A 47.082897
6  1996-01-01         A  3.232268
7  1997-01-01         A 26.877169
8  1998-01-01         A 44.728533
9  1999-01-01         A 28.020316
10 2000-01-01         A 23.374122
11 1991-01-01         B 15.091298
12 1992-01-01         B 39.626952
13 1993-01-01         B 21.039869
14 1994-01-01         B 44.267853
15 1995-01-01         B 47.082897
16 1996-01-01         B  3.232268
17 1997-01-01         B 26.877169
18 1998-01-01         B 44.728533
19 1999-01-01         B 28.020316
20 2000-01-01         B 23.374122

This should do what you want and your pivot_wider should work now:

> DF %>% 
+     pivot_wider(names_from = Parameter, values_from = Value)
# A tibble: 10 × 3
   Date           A     B
   <date>     <dbl> <dbl>
 1 1991-01-01 15.1  15.1 
 2 1992-01-01 39.6  39.6 
 3 1993-01-01 21.0  21.0 
 4 1994-01-01 44.3  44.3 
 5 1995-01-01 47.1  47.1 
 6 1996-01-01  3.23  3.23
 7 1997-01-01 26.9  26.9 
 8 1998-01-01 44.7  44.7 
 9 1999-01-01 28.0  28.0 
10 2000-01-01 23.4  23.4 

Try changing the repeat in the Parameter to c(rep("A", times = 10), rep("B", times=10)), assuming your intention is to have one "A" per year, and one "B" per year.

Compare your original:

library(tidyverse)

set.seed(123)
DF <- data.frame(Date = seq(as.Date("1991-01-01"), 
                            to = as.Date("2000-12-31"), 
                            by = "year"), 
                 Parameter = rep(c("A","B"), times = 10),
                 Value = runif(10,1,50)) %>% 
  pivot_wider(names_from = Parameter, values_from = Value)

DF
#> # A tibble: 10 × 3
#>    Date       A         B        
#>    <date>     <list>    <list>   
#>  1 1991-01-01 <dbl [2]> <NULL>   
#>  2 1992-01-01 <NULL>    <dbl [2]>
#>  3 1993-01-01 <dbl [2]> <NULL>   
#>  4 1994-01-01 <NULL>    <dbl [2]>
#>  5 1995-01-01 <dbl [2]> <NULL>   
#>  6 1996-01-01 <NULL>    <dbl [2]>
#>  7 1997-01-01 <dbl [2]> <NULL>   
#>  8 1998-01-01 <NULL>    <dbl [2]>
#>  9 1999-01-01 <dbl [2]> <NULL>   
#> 10 2000-01-01 <NULL>    <dbl [2]>

With:

DF <- data.frame(Date = seq(as.Date("1991-01-01"), 
                            to = as.Date("2000-12-31"), 
                            by = "year"), 
                 Parameter = c(rep("A", times = 10), rep("B", times=10)),
                 Value = runif(10,1,50)) %>% 
  pivot_wider(names_from = Parameter, values_from = Value)

DF
#> # A tibble: 10 × 3
#>    Date           A     B
#>    <date>     <dbl> <dbl>
#>  1 1991-01-01 47.9  47.9 
#>  2 1992-01-01 23.2  23.2 
#>  3 1993-01-01 34.2  34.2 
#>  4 1994-01-01 29.1  29.1 
#>  5 1995-01-01  6.04  6.04
#>  6 1996-01-01 45.1  45.1 
#>  7 1997-01-01 13.1  13.1 
#>  8 1998-01-01  3.06  3.06
#>  9 1999-01-01 17.1  17.1 
#> 10 2000-01-01 47.8  47.8

^{Created on 2023-08-10 with reprex v2.0.2}