name_spec: Name specifications

In vctrs: Vector Helpers

Name specifications

Description

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
try(vec_c(name = 1:3))  # bad

# They also can't have internal names, even if scalar:
try(vec_c(name = c(internal = 1)))  # bad

# 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}")
vec_c(name = 1:3, other = 4:5, .name_spec = "{outer}_{inner}")

# 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)

# Or purrr-style formulas for anonymous functions:
vec_c(name = 1:3, other = 4:5, .name_spec = ~ paste0(.x, .y))

vctrs documentation built on May 29, 2024, 11:39 a.m.