Why doesn't "+" operate on characters in R?

@ Dirk: For once, you're not quite right. It's not the parser. One can write methods in R for "+" -- help("+") goes to "Arithmetic operators" and mentions that these are generic and you can write methods for them ... and of course many package writers do, e.g., we do for the 'Matrix' package, and I also do for the "Rmpfr" package, e.g. But Dirk is also right (of course!) that you cannot do it in R currently, by just defining a method for "+.character".

About three years ago, I had started a thread on R-devel (the R mailing list on R development; very much recommended if you are interested in these topics; you can also access through Gmane if you don't want to subscribe) :r-devel archived msg

It came to an interesting discussion with quite a few pros and cons, notably John Chambers ("the father of S and hence R") pretty strongly opposing to use "+" for an operation that is not commutative, and also (*) ...../r-devel/2006-August/039012.html (by another R-core member), supporting the view that we (R Core) should not adopt / support the idea; and if people *really wanted it, they could define %+% for that.

((*) Hmm, I can only post one hyperlink as a "new user" ... that's a bit inconvenient)

sprintf is no more convenient in the default case (no formatting) but I should use it more often. Thanks for the suggestion of using "%+%", though this actually does not answer the main question.

Eduardo Leoni 2009-08-23 23:38:25

There is no answer -- you cannot override + as an operator due to the way the parser works. Steve's suggestions is your best bet, apart from maybe defining a shortcut function p <- function(...) paste(..., sep="") which may be easier to type than the usual paste() with sep="".

Dirk Eddelbuettel 2009-08-24 02:01:37

Okay, so we finally found a counter example to fortune(109). More accurately, the answer is "write your own damn parser" :)

Eduardo Leoni 2009-08-24 03:09:30

I noticed Hadley wrote some methods for "+" in his ggplot2 package. There is is used to add multiple layers on a plot.

Thierry 2009-08-24 11:00:31

Martin, thanks for the detailed correction.

Dirk Eddelbuettel 2009-08-24 11:21:13

Excellent thread you started there, thanks! There seems to be a conflict between those that don't believe that it is natural to think of "+" as concatenation (e.g. Chambers) and those that see it all the time in other languages and are used to it. Has the discussion simply stopped there?

Eduardo Leoni 2009-08-24 14:59:35

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Why doesn't "+" operate on characters in R?

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