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
library(tibble)
Vectors of size 1 are recycled to the size of any other vector:
tibble(x = 1:3, y = 1L)
This includes vectors of size 0:
tibble(x = integer(), y = 1L)
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)
Packages in r-lib and the tidyverse generally use [vec_size_common()] and [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") vec_recycle_common(1:3, "x") vec_size_common(1:3, c("x", "y"))
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 vignette("type-size")
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