[Rd] "+" operator on characters revisited

Gabor Grothendieck ggrothendieck at gmail.com
Sun Jan 23 13:34:07 CET 2011

On Sun, Jan 23, 2011 at 6:56 AM, Vitalie S. <spinuvit.list at gmail.com> wrote:
> Gabor Grothendieck <ggrothendieck at gmail.com> writes:
>> On Sat, Jan 22, 2011 at 3:08 PM, Vitalie S. <spinuvit.list at gmail.com> wrote:
>>> Hello everyone!
>>> Motivated by the recent post on SO
>> http://stackoverflow.com/questions/4730551/making-a-string-concatenation-operator-in-r>
>>> I wonder what is the current state of argument on making "+" to
>>> concatenate character vectors. The "+" method is still sealed for
>>> signature("character", "character") in the current version of R.
>>> The 4 years old R-devel thread
>>> https://www.stat.math.ethz.ch/pipermail/r-devel/2006-August/038991.html>
>>> on the same topic, stopped without reaching any definite conclusion.
>>> The only definite argument occurred in the thread against "+" operator
>>> was the lack of commutativity (as if one have to prove algebraic
>>> theorems in R).
>>> Yet another useful suggestion of introducing cat0() and paste0(), for
>>> the common use of cat and paste with sep="" was not absorbed by the
>>> core R either.
>> The gsubfn package has always had a paste0 function and I would be
>> happy to remove it if the core adds it.
>> Also the gsubfn supports quasi perl style string interpolation that
>> can sometimes be used to avoid the use of paste in the first place.
>> Just preface the function in question by fn$ like this:
>> library(gsubfn)
>> fn$cat("pi = $pi\n")
> Thanks for the tip. Not bad indeed.
> Almost as readable as
> cat("pi = " + pi + "\n")

To me the + can be substantially less readable.  The need to
repeatedly quote everything makes it just as bad as paste.  Compare
the following and try to figure out if there is an error in quoting in
the + and paste solutions.  Trying to distinguish the single and
double quotes is pretty difficult but simple in the fn$ and sprintf
solutions.  Even if there were no quotes the constant need to
interpose quotes makes it hard to read.

library(sqldf) # also pulls in gsubfn which has fn$ and paste0
plant <- "Qn1"
treatment <- "nonchilled"

# using +
# sqldf("select * from CO2 where Plant = '" + plant + "' and Treatment
= '" + treatment + "' limit 10")

# using paste0, also from gsubfn
sqldf(paste0("select * from CO2 where Plant = '", plant, "' and
Treatment = '", treatment, "' limit 10"))

# using paste, almost the same as last one
sqldf(paste("select * from CO2 where Plant = '", plant, "' and
Treatment = '", treatment, "' limit 10", sep = ""))

# With the perl-like interpolation you don't need the repeated quoting
in the first place so its much clearer.

# using perl-like interpolation from gsubfn
fn$sqldf("select * from CO2 where Plant = '$plant' and Treatment =
'$treatment' limit 10")

# sprintf is nearly as good as the perl-like interpolation except you
have to match up % codes and arguments which is a bit of nuisance #
and there are more parentheses.  On the other hand it does have the
advantage that there is the facility for fancier formatting codes
# (though this example does not illustrate that aspect):

# using sprintf
sqldf(sprintf("select * from CO2 where Plant = '%s' and Treatment =
'%s' limit 10", plant, treatment))

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