Pop an Element by Position

Returns the selected element and the remaining sequence.

Usage

pop_at(x, index)

Arguments

x

A flexseq.

index

One-based position to remove.

Value

A list with fields:

• value: the element at index, or NULL when index is out of bounds.

• remaining: the sequence after removing the selected element.

Details

This operation is persistent: x is not modified.

Positive integer indices beyond length(x) return a non-throwing miss object with value = NULL and remaining = x. Invalid indices (NA, non-integer, <= 0, or length not equal to 1) error.

Examples

x <- flexseq("a", "b", "c", "d")
out <- pop_at(x, 3)
out$value
#> [1] "c"
out$remaining
#> Unnamed flexseq with 3 elements.
#> 
#> Elements:
#> 
#> [[1]]
#> [1] "a"
#> 
#> [[2]]
#> [1] "b"
#> 
#> [[3]]
#> [1] "d"
#> 
x  # unchanged
#> Unnamed flexseq with 4 elements.
#> 
#> Elements:
#> 
#> [[1]]
#> [1] "a"
#> 
#> [[2]]
#> [1] "b"
#> 
#> [[3]]
#> [1] "c"
#> 
#> [[4]]
#> [1] "d"
#> 

pop_at(x, 10)
#> $value
#> NULL
#> 
#> $remaining
#> Unnamed flexseq with 4 elements.
#> 
#> Elements:
#> 
#> [[1]]
#> [1] "a"
#> 
#> [[2]]
#> [1] "b"
#> 
#> [[3]]
#> [1] "c"
#> 
#> [[4]]
#> [1] "d"
#> 
#> 
try(pop_at(x, 0))
#> Error in .ft_validate_scalar_position_missable(index, n) : 
#>   Only positive integer indices are supported.