Recycling rules used by r-lib and the tidyverseSource:
Recycling describes the concept of repeating elements of one vector to match the size of another. There are two rules that underlie the "tidyverse" recycling rules:
Vectors of size 1 will be recycled to the size of any other vector
Otherwise, all vectors must have the same size
Vectors of size 1 are recycled to the size of any other vector:
tibble(x = 1:3, y = 1L) #> # A tibble: 3 x 2 #> x y #> <int> <int> #> 1 1 1 #> 2 2 1 #> 3 3 1
This includes vectors of size 0:
If vectors aren't size 1, they must all be the same size. Otherwise, an error is thrown:
tibble(x = 1:3, y = 4:7) #> Error in `tibble()`: #> ! Tibble columns must have compatible sizes. #> * Size 3: Existing data. #> * Size 4: Column `y`. #> i Only values of size one are recycled.
Packages in r-lib and the tidyverse generally use
vec_recycle_common() as the backends for handling recycling rules.
vec_size_common()returns the common size of multiple vectors, after applying the recycling rules
vec_recycle_common()goes one step further, and actually recycles the vectors to their common size
vec_size_common(1:3, "x") #>  3 vec_recycle_common(1:3, "x") #> [] #>  1 2 3 #> #> [] #>  "x" "x" "x" vec_size_common(1:3, c("x", "y")) #> Error: #> ! Can't recycle `..1` (size 3) to match `..2` (size 2).
Base R recycling rules
The recycling rules described here are stricter than the ones generally used by base R, which are:
If any vector is length 0, the output will be length 0
Otherwise, the output will be length
max(length_x, length_y), and a warning will be thrown if the length of the longer vector is not an integer multiple of the length of the shorter vector.
We explore the base R rules in detail in