A name specification describes how to combine an inner and outer names. This sort of name combination arises when concatenating vectors or flattening lists. There are two possible cases:
Named vector:
vec_c(outer = c(inner1 = 1, inner2 = 2))Unnamed vector:
vec_c(outer = 1:2)
In r-lib and tidyverse packages, these cases are errors by default, because there's no behaviour that works well for every case. Instead, you can provide a name specification that describes how to combine the inner and outer names of inputs. Name specifications can refer to:
outer: The external name recycled to the size of the input vector.inner: Either the names of the input vector, or a sequence of integer from 1 to the size of the vector if it is unnamed.
Arguments
- name_spec, .name_spec
A name specification for combining inner and outer names. This is relevant for inputs passed with a name, when these inputs are themselves named, like
outer = c(inner = 1), or when they have length greater than 1:outer = 1:2. By default, these cases trigger an error. You can resolve the error by providing a specification that describes how to combine the names or the indices of the inner vector with the name of the input. This specification can be:A function of two arguments. The outer name is passed as a string to the first argument, and the inner names or positions are passed as second argument.
An anonymous function as a purrr-style formula.
A glue specification of the form
"{outer}_{inner}".An
rlang::zap()object, in which case both outer and inner names are ignored and the result is unnamed.
See the name specification topic.
Examples
# By default, named inputs must be length 1:
vec_c(name = 1) # ok
#> name
#> 1
try(vec_c(name = 1:3)) # bad
#> Error in vec_c(name = 1:3) :
#> Can't merge the outer name `name` with a vector of length > 1.
#> Please supply a `.name_spec` specification.
# They also can't have internal names, even if scalar:
try(vec_c(name = c(internal = 1))) # bad
#> Error in vec_c(name = c(internal = 1)) :
#> Can't merge the outer name `name` with a named vector.
#> Please supply a `.name_spec` specification.
# Pass a name specification to work around this. A specification
# can be a glue string referring to `outer` and `inner`:
vec_c(name = 1:3, other = 4:5, .name_spec = "{outer}")
#> name name name other other
#> 1 2 3 4 5
vec_c(name = 1:3, other = 4:5, .name_spec = "{outer}_{inner}")
#> name_1 name_2 name_3 other_1 other_2
#> 1 2 3 4 5
# They can also be functions:
my_spec <- function(outer, inner) paste(outer, inner, sep = "_")
vec_c(name = 1:3, other = 4:5, .name_spec = my_spec)
#> name_1 name_2 name_3 other_1 other_2
#> 1 2 3 4 5
# Or purrr-style formulas for anonymous functions:
vec_c(name = 1:3, other = 4:5, .name_spec = ~ paste0(.x, .y))
#> name1 name2 name3 other1 other2
#> 1 2 3 4 5