Name specifications — name

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

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.

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 : 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 : Can't merge the outer name `name` with a vector of length > 1.
#> 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