Operation overloading in R

Question

What's the most straight forward way of overloading '+' for characters? I have defined '%+%' <- function(...) paste(...,sep=""):

str <- "aa"%+%"bb"%+%"cc" #str="aabbcc"

But I don't like the syntax. I think str <- "aa"+"bb"+"cc" would be nicer.

(I am building long SQL queries to use with RODBC, the usual paste is not very handy in such situations. Any suggestions?)

@David Heffernan It does. But does not allow to redefine some object (functions, operators, constants). [Check another question about it on stackoverflow](http://stackoverflow.com/questions/1319698/why-doesnt-operate-on-characters-in-r). — Marek, Mar 16 '11 at 16:21

score 11 · Answer 1 · answered Mar 16 '11 at 08:37

11

You may try something like that :

R> oldplus <- `+`
R> `+` <- function(e1, e2) { 
R>     if (is.character(e1) && is.character(e2)) { 
R>          paste(e1,e2,sep="") 
R>      }
R>      else { 
R>          oldplus(e1,e2) 
R>      } 
R>  }

Which gives :

R> 2+3
[1] 5
R> "aa"+"bb"
[1] "aabb"

But as Sacha pointed out, overloading such a basic function is very dangerous, and I can't assure you it will not break your R session and make your computer explode :-)

answered Mar 16 '11 at 08:37

juba

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Should be fine, but you have to remember to `rm()` the overloaded function. (S)he has been warned. :) – Roman Luštrik Mar 16 '11 at 09:54

score 5 · Accepted Answer · answered Mar 16 '11 at 08:29

5

I think that using two arguments is better than the dots:

'%+%' <- function(x,y) paste(x,y,sep="")

"a"%+%"b"%+%"C"
[1] "abC"

If you really really want to you can overwrite +, but be veeeeery careful when doing this as you will break one of the most important functions in R. I can't think of any reason why you would want to do that over %+%:

# '+' <- function(x,y) paste(x,y,sep="")
# "a"+"b"+"C"
# [1] "abC"

rm('+')

commented it out to be sure I don't accidently break someones R:)

answered Mar 16 '11 at 08:29

Sacha Epskamp

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The proper way to do this is to define the operator on a particular class like `+.SQL` then to define your vector as having that class. That way you can't break the function for everyone else. See http://stackoverflow.com/a/4731547/245022 – adamleerich Jul 23 '12 at 14:15
If you're concerend about safety, wouldn't it be better to limit the overload on a string class? like `'+'.string <- function(` – JonnyRobbie Oct 04 '19 at 22:10

score 2 · Answer 3 · answered Mar 16 '11 at 11:11

Why is the usual 'paste' not very handy? It's what it's meant for. Suggestions:

Write yourself an unusual paste function that does what you want. Maybe you just don't like typing 'sep=""' all the time. So write a function that calls paste with sep="". Or whatever.

Building long SQL queries with string concatenation is potential fail anyway. See http://xkcd.com/327/ for the canonical example.

Another possibility is some kind of templating solution. I've used the brew package in the past and it's great for that.

`So write a function that calls paste with sep="".` But that's what `paste0()` is for! — Gaffi, Mar 14 '18 at 15:07

score 0 · Answer 4 · answered Mar 19 '14 at 12:49

0

You can find this operator in stringi package.

http://docs.rexamine.com/R-man/stringi/oper_plus.html

answered Mar 19 '14 at 12:49

bartektartanus

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Operation overloading in R

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