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make.names {base}

Make Syntactically Valid Names
R 3.0.2


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, OS X 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 (for example, S-PLUS and some DBMSs).


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( !=] # those 10 with a space

Documentation reproduced from R 3.0.2. License: GPL-2.