vec_as_names() takes a character vector of names and repairs it according to the repair argument. It is the r-lib and tidyverse equivalent of base::make.names().

vctrs deals with a few levels of name repair:

  • minimal names exist. The names attribute is not NULL. The name of an unnamed element is "" and never NA. For instance, vec_as_names() always returns minimal names and data frames created by the tibble package have names that are, at least, minimal.

  • unique names are minimal, have no duplicates, and can be used where a variable name is expected. Empty names, and ... or .. followed by a sequence of digits are banned.

    • All columns can be accessed by name via df[["name"]] and df$`name` and with(df, `name`).

  • universal names are unique and syntactic (see Details for more).

universal implies unique, unique implies minimal. These levels are nested.

vec_as_names(
  names,
  ...,
  repair = c("minimal", "unique", "universal", "check_unique"),
  quiet = FALSE
)

Arguments

names

A character vector.

...

These dots are for future extensions and must be empty.

repair

Either a string or a function. If a string, it must be one of "check_unique", "minimal", "unique", or "universal". If a function, it is invoked with a vector of minimal names and must return minimal names, otherwise an error is thrown.

  • Minimal names are never NULL or NA. When an element doesn't have a name, its minimal name is an empty string.

  • Unique names are unique. A suffix is appended to duplicate names to make them unique.

  • Universal names are unique and syntactic, meaning that you can safely use the names as variables without causing a syntax error.

The "check_unique" option doesn't perform any name repair. Instead, an error is raised if the names don't suit the "unique" criteria.

quiet

By default, the user is informed of any renaming caused by repairing the names. This only concerns unique and universal repairing. Set quiet to TRUE to silence the messages.

minimal names

minimal names exist. The names attribute is not NULL. The name of an unnamed element is "" and never NA.

Examples:

Original names of a vector with length 3: NULL
                           minimal names: "" "" ""

                          Original names: "x" NA
                           minimal names: "x" ""

unique names

unique names are minimal, have no duplicates, and can be used (possibly with backticks) in contexts where a variable is expected. Empty names, and ... or .. followed by a sequence of digits are banned If a data frame has unique names, you can index it by name, and also access the columns by name. In particular, df[["name"]] and df$`name` and also with(df, `name`) always work.

There are many ways to make names unique. We append a suffix of the form ...j to any name that is "" or a duplicate, where j is the position. We also change ..# and ... to ...#.

Example:

Original names:     ""     "x"     "" "y"     "x"  "..2"  "..."
  unique names: "...1" "x...2" "...3" "y" "x...5" "...6" "...7"

Pre-existing suffixes of the form ...j are always stripped, prior to making names unique, i.e. reconstructing the suffixes. If this interacts poorly with your names, you should take control of name repair.

universal names

universal names are unique and syntactic, meaning they:

  • Are never empty (inherited from unique).

  • Have no duplicates (inherited from unique).

  • Are not .... Do not have the form ..i, where i is a number (inherited from unique).

  • Consist of letters, numbers, and the dot . or underscore _ characters.

  • Start with a letter or start with the dot . not followed by a number.

  • Are not a reserved word, e.g., if or function or TRUE.

If a vector has universal names, variable names can be used "as is" in code. They work well with nonstandard evaluation, e.g., df$name works.

vctrs has a different method of making names syntactic than base::make.names(). In general, vctrs prepends one or more dots . until the name is syntactic.

Examples:

 Original names:     ""     "x"    NA      "x"
universal names: "...1" "x...2" "...3" "x...4"

  Original names: "(y)"  "_z"  ".2fa"  "FALSE"
 universal names: ".y." "._z" "..2fa" ".FALSE"

See also

rlang::names2() returns the names of an object, after making them minimal.

The Names attribute section in the "tidyverse package development principles".

Examples

# By default, `vec_as_names()` returns minimal names: vec_as_names(c(NA, NA, "foo"))
#> [1] "" "" "foo"
# You can make them unique: vec_as_names(c(NA, NA, "foo"), repair = "unique")
#> New names: #> * NA -> ...1 #> * NA -> ...2
#> [1] "...1" "...2" "foo"
# Universal repairing fixes any non-syntactic name: vec_as_names(c("_foo", "+"), repair = "universal")
#> New names: #> * `_foo` -> ._foo #> * `+` -> .
#> [1] "._foo" "."