On Fri, 19 Mar 2010, Paul Johnson wrote:
I don't know anybody who has S-plus these days, but I expect some of
you might, and perhaps you won't mind telling me something.
I'm working on my presentation about R for the general audience. As I
survey the suggestions from this list about that project, I find
myself wondering whether S-plus benefits from R. Does S-plus syntax
change like R's does. I can take code for S and run it through R, but
if I took some R code to an S-plus system, would it work?
Example 1. _, <-, =
The old S documents I find emphasize assigment with "_".
When I started with R, that was deprecated, then forbidden. "_" was
not allowed in file names, now it is. It was absolutely necessary to
use <-. = caused errors. Around the time of R-2.1 or so, it became
possible to run R code that has = for assignments. It's not encouraged
by R core team, but = is allowed.
I don't think that the R core team has any position on this. Some of them use
=, some don't
Does S+ now accept either
<-
or
=
?
Yes. This change happened in S4, then S-PLUS, then R.
Example 2. Semicolons now discouraged in R code.
We used to require ; to end commands.
Now the R parser is smart enough to spot line breaks and interpret
them accordingly. R's been that way for as long as I can remember, but
I think the ; was required in earliest R releases.
I really don't think so. Now, I didn't use the *earliest* releases, but I did
use R 0.16, which was quite a long time ago, and I don't remember semicolons
being required or even encouraged.
They are permitted in both S and R, but most people seem to use them only when
writing one-line functions.
Example 3. Namespace. Does S-plus get better as R does?
Years ago, I was modeling US Democrats and Republicans and I created
an indicator variable called "rep". regression models would not work
after that because the rep function had been blocked. It was very
frustrating to me.
Professor Ripley spotted the error and posed a message called "Don't
use the names of R functions as variable names"
http://www.mail-archive.com/r-h...@stat.math.ethz.ch/msg11585.html.
After that, I was terrified that any name I used might conflict with a
built in R function name.
Last month, i saw a student here with a political model and he used
rep as a variable in a regression model, it seemed to work just fine.
I surmise that the rise in usage of namespaces in R packages accounts
for that?
No, this was fixed much, much earlier than package namespaces. Symbol lookup
when a function is needed can specify that a function is desired. I think this
has also been true in S-PLUS for a long time, but I'm not completely sure.
There are just a few places where problems can occur, such as do.call() with an
unquoted function name, where a user-defined variable can get in the way.
-thomas
Thomas Lumley Assoc. Professor, Biostatistics
tlum...@u.washington.edu University of Washington, Seattle
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