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

[ikarus]

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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