R: Make Syntactically Valid Names

make.names {base} | R Documentation

## Make Syntactically Valid Names

### Description

Make syntactically valid names out of character vectors.

### Usage

    make.names(names, unique = FALSE, allow_ = TRUE)

### Arguments

`names` | character vector to be coerced to syntactically valid names. This is coerced to character if necessary.
`unique` | logical; if `TRUE`, the resulting elements are unique. This may be desired for, e.g., column names.
`allow_` | logical. For compatibility with R prior to 1.9.0.

### Details

A syntactically valid name consists of letters, numbers and the dot or underline characters and starts with a letter or the dot not followed by a number. Names such as `".2way"` are not valid, and neither are the reserved words.

The definition of a letter depends on the current locale, but only ASCII digits are considered to be digits.

The character `"X"` is prepended if necessary. All invalid characters are translated to `"."`. A missing value is translated to `"NA"`. Names which match R keywords have a dot appended to them. Duplicated values are altered by `make.unique`.

### Value

A character vector of same length as `names` with each changed to a syntactically valid name, in the current locale's encoding.

### Warning

Some OSes, notably FreeBSD, report extremely incorrect information about which characters are alphabetic in some locales (typically, all multi-byte locales including UTF-8 locales). However, R provides substitutes on Windows, OS X and AIX.

### Note

Prior to R version 1.9.0, underscores were not valid in variable names, and code that relies on them being converted to dots will no longer work. Use `allow_ = FALSE` for back-compatibility.

`allow_ = FALSE` is also useful when creating names for export to applications which do not allow underline in names (for example, S-PLUS and some DBMSs).

### See Also

`make.unique`, `names`, `character`, `data.frame`.

### Examples

    make.names(c("a and b", "a-and-b"), unique = TRUE)
    # "a.and.b"  "a.and.b.1"
    make.names(c("a and b", "a_and_b"), unique = TRUE)
    # "a.and.b"  "a_and_b"
    make.names(c("a and b", "a_and_b"), unique = TRUE, allow_ = FALSE)
    # "a.and.b"  "a.and.b.1"
    make.names(c("", "X"), unique = TRUE)
    # "X.1" "X" currently; R up to 3.0.2 gave "X" "X.1"

    state.name[make.names(state.name) != state.name] # those 10 with a space

[Package base version 3.1.2 Index]