make.names {base}R Documentation

Make Syntactically Valid Names


Make syntactically valid names out of character vectors.


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



character vector to be coerced to syntactically valid names. This is coerced to character if necessary.


logical; if TRUE, the resulting elements are unique. This may be desired for, e.g., column names.


logical. For compatibility with R prior to 1.9.0.


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.


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


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, macOS and AIX.


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 (such as some DBMSes).

See Also

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


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"[make.names( !=] # those 10 with a space

[Package base version 4.4.1 Index]