Vector recycling

vec_recycle(x, size) recycles a single vector to given size. vec_recycle_common(...) recycles multiple vectors to their common size. All functions obey the vctrs recycling rules, described below, and will throw an error if recycling is not possible. See vec_size() for the precise definition of size.

vec_recycle(x, size)

vec_recycle_common(..., .size = NULL)

Arguments

x, ...	Vectors to recycle.
size	Desired output size.
.size	Desired output size. If omitted, will use the common size from vec_size_common().

Recycling rules

The common size of two vectors defines the recycling rules, and can be summarise with the following table:

(Note NULLs are handled specially; they are treated like empty arguments and hence don't affect the size)

This is a stricter set of rules than base R, which will usually return output of length max(nx, ny), warning if the length of the longer vector is not an integer multiple of the length of the shorter.

We say that two vectors have compatible size if they can be recycled to be the same length.

Examples

# Inputs with 1 observation are recycled
vec_recycle_common(1:5, 5)
#> [[1]]
#> [1] 1 2 3 4 5
#> 
#> [[2]]
#> [1] 5 5 5 5 5
#> 
vec_recycle_common(integer(), 5)
#> [[1]]
#> integer(0)
#> 
#> [[2]]
#> numeric(0)
#> 
if (FALSE) {
vec_recycle_common(1:5, 1:2)
}

# Data frames and matrices are recycled along their rows
vec_recycle_common(data.frame(x = 1), 1:5)
#> [[1]]
#>   x
#> 1 1
#> 2 1
#> 3 1
#> 4 1
#> 5 1
#> 
#> [[2]]
#> [1] 1 2 3 4 5
#> 
vec_recycle_common(array(1:2, c(1, 2)), 1:5)
#> [[1]]
#>      [,1] [,2]
#> [1,]    1    2
#> [2,]    1    2
#> [3,]    1    2
#> [4,]    1    2
#> [5,]    1    2
#> 
#> [[2]]
#> [1] 1 2 3 4 5
#> 
vec_recycle_common(array(1:3, c(1, 3, 1)), 1:5)
#> [[1]]
#> , , 1
#> 
#>      [,1] [,2] [,3]
#> [1,]    1    2    3
#> [2,]    1    2    3
#> [3,]    1    2    3
#> [4,]    1    2    3
#> [5,]    1    2    3
#> 
#> 
#> [[2]]
#> [1] 1 2 3 4 5
#>