Variable name restrictions in R

Question

What are the restrictions as to what characters (and maybe other restrictions) can be used for a variable name in R?

(This screams of general reference, but I can't seem to find the answer)

Answer 1

You might be looking for the discussion from ?make.names:

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.

In the help file itself, there's a link to a list of reserved words, which are:

if else repeat while function for in next break

TRUE FALSE NULL Inf NaN NA NA_integer_ NA_real_ NA_complex_ NA_character_

Many other good notes from the comments include the point by James to the R FAQ addressing this issue and Josh's pointer to a related SO question dealing with checking for syntactically valid names.

Answer 2

Almost NONE! You can use 'assign' to make ridiculous variable names:

assign("1",99) ls() # [1] "1" 

Yes, that's a variable called '1'. Digit 1. Luckily it doesn't change the value of integer 1, and you have to work slightly harder to get its value:

1 # [1] 1 get("1") # [1] 99 

The "syntactic restrictions" some people might mention are purely imposed by the parser. Fundamentally, there's very little you can't call an R object. You just can't do it via the '<-' assignment operator. "get" will set you free :)