[R] break string at specified possitions

[Daniel Nordlund]

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


Hope this is helpful,

Dan

Daniel Nordlund
Bothell, WA USA