[R] break string at specified possitions

[Martin Maechler]

> On 5/11/2016 2:23 PM, Jan Kacaba wrote:
> > Here is my attempt at function which computes margins from positions.
> >
> > require("stringr")
> > require("dplyr")
> >
> > ends<-seq(10,100,8)  # end margins
> > test_string<-"Lorem ipsum dolor sit amet, consectetuer adipiscing
> > elit. Aliquam in lorem sit amet leo accumsan lacinia."
> >
> > sekoj=function(ends){
> >   l_ends<-length(ends)
> >   begs=vector(mode="integer",l_ends)
> >   begs[1]=1
> >   for (i in 2:(l_ends)){
> >     begs[i]<-ends[i-1]+1
> >   }
> >   margs<-rbind(begs,ends)
> >   margs<-cbind(margs,c(ends[l_ends]+1,-1))
> >   #rownames(margs)<-c("beg","end")
> >   return(margs)
> > }
> > margins<-sekoj(ends)
> > str_sub(test_string,margins[1,],margins[2,]) %>% print
> >
> > Code to run in browser:
> > http://www.r-fiddle.org/#/fiddle?id=rVmNVxDV
> >
> > 2016-05-11 23:12 GMT+02:00 Bert Gunter <bgunter.4567 at gmail.com>:
> >> Dunno -- but you might have a look at Hadley Wickham's 'stringr' package:
> >> https://cran.r-project.org/web/packages/stringr/stringr.pdf
> >>
> >> Cheers,
> >>
> >> Bert
> >>
> >>
> >> Bert Gunter
> >>
> >> "The trouble with having an open mind is that people keep coming along
> >> and sticking things into it."
> >> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
> >>
> >>
> >> On Wed, May 11, 2016 at 1:12 PM, Jan Kacaba <jan.kacaba at gmail.com> wrote:
> >>> Dear R-help
> >>>
> >>> I would like to split long string at specified precomputed positions.
> >>> 'substring' needs beginings and ends. Is there a native function which
> >>> accepts positions so I don't have to count second argument?
> >>>
> >>> For example I have vector of possitions pos<-c(5,10,19). Substring
> >>> needs input first=c(1,6,11) and last=c(5,10,19). There is no problem
> >>> to write my own function. Just asking.
> >>>
> >>> Derek
> >>>
> 
> I think you can simply this. just create a function (I'll call it begs) 
> to compute the beginning positions.
> 
>      begs <- function(x) c(0,x[-length(x)])+1
> 
> Then, then use that function in your call to str_sub
> 
>      str_sub(test_string,begs(ends),ends) %>% print
> 

and why can't you simply use base R's  substr() function ?
Packages (such as 'stringr' in this case) have their uses and
great merits, but using base R seems more sensical to me (also
slightly more future-proof).


> Hope this is helpful,

Yes, I'd think so , because that was also my quick thought when
I read the OP's question.

Martin


--
Martin Maechler, ETH Zurich & R Core