[R] How to create a string containing '\/' to be used with SED?

[David Winsemius]

What do you mean by "doesn't work" and "the \\" are removed?

 > a <- "..\\/path\\/file"

 > a
[1] "..\\/path\\/file"

 > cat(a)
..\/path\/file

--  
David Winsemius

On Nov 26, 2008, at 7:46 PM, ikarus wrote:

>
> Thanks Sean!!
>
> I followed you suggestion to use gsub() and it worked perfectly!
> I still can't create a string with inside "\/"  (e.g., a <-
> "..\\/path\\/file"
> doesn't work, R complains and the \\ are removed), but I don't care,
> gsub() does the same job as sed and without using any system call.
>
>
>
> seanpor wrote:
>>
>> Good morning,
>>
>> You do not need to quote a forward slash / in R, but you do need to  
>> quote
>> a backslash when you're inputting it... so to get a string which  
>> actually
>> contains "blah\/blah"... you need to use "blah\\/blah"
>>
>> http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-does-backslash-behave-strangely-inside-strings_003f
>>
>> Unless this is a very very big file you shouldn't need to go out to  
>> sed,
>> as gsub() should work adequately... and probably quicker and  
>> cleaner.  So
>> something along the lines of.. (UNTESTED!!! since I don't have a
>> reproduceable example)
>>
>> tmp1 <- readLines(configurationFile)
>> tmp1 <- gsub("^instance .*", paste("instance = ", data 
>> $instancePath, "/",
>> data$newInstance, sep = ""), tmp1)
>>
>>
>> I'm working on 50mb text files, and doing all sorts of  
>> manipulations and I
>> do it all inside R under windows XP...  reading a 50mb text file  
>> across
>> the 100mb network and doing a gsub() on most lines takes an elapsed  
>> 16
>> seconds on this office desktop.
>>
>> hth...
>>
>> Regards,
>> Sean
>>
>>
>> ikarus wrote:
>>>
>>> Hi guys,
>>> I've been struggling to find a solution to the following issue:
>>> I need to change strings in .ini files that are given in input to a
>>> program whose output is processed by R. The strings to be changed  
>>> looks
>>> like:
>>> "instance = /home/TSPFiles/TSPLIB/berlin52.tsp"
>>>
>>> I normally use Sed for this kind of things. So, inside R I'd like to
>>> write something like:
>>>
>>> command <- paste("sed -i 's/^instance .*/instance = ",
>>> data$instancePath,
>>>                   data$newInstance, "/' ", configurationFile, sep  
>>> = "")
>>> system(command)
>>>
>>> This will overwrite the line starting with "instance " using  
>>> "instance =
>>> the_new_instance"
>>> In the example I gave, data$instancePath = /home/TSPFiles/TSPLIB/  
>>> and
>>> data$newInstance = berlin52.tsp
>>>
>>> The problem is that I need to pass the above path string to sed in  
>>> the
>>> form:
>>> "\/home\/TSPFiles\/TSPLIB\/"
>>>
>>> However, I couldn't find a way to "create" such a string in R. I  
>>> tried in
>>> several different ways,
>>> but it always complains saying that '\/' is an unrecognized escape!
>>>
>>> Any suggestion?
>>>
>>> Thanks!
>>>
>>
>
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