[R] = or <-

Erik Iverson iverson at biostat.wisc.edu
Mon Jun 2 16:30:19 CEST 2008

Sébastien wrote:
> Dear R-users,
> I have written a short VB application to clean and format my R code. 
> Everything works fine except one small issue that I did not expected; it 
> is related the automatic replacement of assignment signs from "=" to 
> "<-". Most functions or arguments seem to accept either = or <-, but 
> some don't (e.g.  ls(all=TRUE)). The result is that my supposedly clean 
> codes do not run anymore :-(
> Is there a way to know the list of arguments/functions that do not 
> accept "<-" signs ?

You are surely mixing two concepts here.

When you are doing an assignment of a value to a variable, you may use 
either <- or =.  Example

a <- 2
a = 2

both bind the value of 2 to the symbol "a".

When you call a function, for example ls, you can specify the argument 
names, such as ls(all = TRUE).

If you attempted ls(all <- TRUE), the value of TRUE will be assigned to 
the symbol 'all', and then ls will be evaluated with its first argument 
"names" as TRUE, which produces your error.  You almost certainly want 
ls(all = TRUE).  After the error, try typing 'all' at the R prompt.  The 
'all' function definition has now been overwritten and is simply TRUE, 
which you probably do not want either.

So, there really is no concept of whether or not a function "accepts <- 
signs".  You want to use = in your function calls, since the '<-' method 
is actually assigning values.

Hope that helps,

> Thanks in advance.
> Sebastien
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