Re: [Rd] attach and object masking

From: Prof Brian Ripley <>
Date: Fri 10 Jun 2005 - 16:32:43 GMT

On Fri, 10 Jun 2005, Martyn Plummer wrote:

> The library() function prints an information message when objects are
> masked on the search path by (or from) a newly attached package. The
> attach() function, however, doesn't. Is there a good reason for this?
> I have adapted the machinery for checking conflicts used in the library
> () function to attach(). If there are no objections, I will check this
> into R-devel.
> I have seen new users get into terrible trouble with attach, e.g.
> 1) attaching the same database multiple times, or
> 2) Masking a vector in an attached data frame with a transformed version
> in the global environment and *then* re-running a script that transforms
> the transformed variable. For example, run this snippet twice and you
> might get a surprise.
> foo <- data.frame(x=1:10)
> attach(foo)
> x <- x/2
> A warning would certainly help.
> Incidentally, (1) occurs in the example for the beavers data set. I
> didn't find any other problems.

Not so: it attaches different dfs with the same column names. I think that is quite common and normally intentional. (Not cleaning up is not good practice though, and that example can be improved a lot.) mailing list Received on Sat Jun 11 02:35:52 2005

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